Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757058AbYJQPpO (ORCPT ); Fri, 17 Oct 2008 11:45:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756077AbYJQPoJ (ORCPT ); Fri, 17 Oct 2008 11:44:09 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:51065 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757365AbYJQPoC (ORCPT ); Fri, 17 Oct 2008 11:44:02 -0400 Date: Fri, 17 Oct 2008 08:43:49 -0700 From: "Paul E. McKenney" To: Gautham R Shenoy Cc: linux-kernel@vger.kernel.org, cl@linux-foundation.org, mingo@elte.hu, akpm@linux-foundation.org, manfred@colorfullife.com, dipankar@in.ibm.com, josht@linux.vnet.ibm.com, schamp@sgi.com, niv@us.ibm.com, dvhltc@us.ibm.com, laijs@cn.fujitsu.com, rostedt@goodmis.org, peterz@infradead.org, penberg@cs.helsinki.fi, andi@firstfloor.org, tglx@linutronix.de Subject: Re: [PATCH, RFC] v7 scalable classic RCU implementation Message-ID: <20081017154349.GF6706@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20080821234318.GA1754@linux.vnet.ibm.com> <20080825000738.GA24339@linux.vnet.ibm.com> <20080830004935.GA28548@linux.vnet.ibm.com> <20080905152930.GA8124@linux.vnet.ibm.com> <20080915160221.GA9660@linux.vnet.ibm.com> <20080923235340.GA12166@linux.vnet.ibm.com> <20081010160930.GA9777@linux.vnet.ibm.com> <20081017083452.GA23228@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081017083452.GA23228@in.ibm.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 117046 Lines: 3117 On Fri, Oct 17, 2008 at 02:04:52PM +0530, Gautham R Shenoy wrote: > On Fri, Oct 10, 2008 at 09:09:30AM -0700, Paul E. McKenney wrote: > > Hello! > Hi Paul, > > Looks interesting. Couple of minor nits. Comments interspersed. Search for "=>" Thank you for looking this over, and especially for noting several issues! Responses interspersed. Thanx, Paul > > This patch fixes a long-standing performance bug in classic RCU that > > results in massive lock contention on the internal RCU lock on systems > > with more than a few hundred CPUs. Although this patch creates a > > separate flavor of RCU for easy of review and patch maintenance, it > > is intended to replace classic RCU. > > > > Still experimental, not for inclusion, but getting quite close. I expect > > to have it in shape for 2.6.29. Definitely ready for -serious- testing > > and abuse. In particular, experience on an actual 1000+ CPU machine > > would be most welcome, and still appears to be forthcoming... > > > > Updates from v6 (http://lkml.org/lkml/2008/9/23/448): > > > > o Fix a number of checkpatch.pl complaints. > > > > o Apply review comments from Ingo Molnar and Lai Jiangshan > > on the stall-detection code. > > > > o Fix several bugs in !CONFIG_SMP builds. > > > > o Fix a misspelled config-parameter name so that RCU now announces > > at boot time if stall detection is configured. > > > > o Run tests on numerous combinations of configurations parameters, > > which after the fixes above, now build and run correctly. > > > > Updates from v5 (http://lkml.org/lkml/2008/9/15/92, bad subject line): > > > > o Fix a compiler error in the !CONFIG_FANOUT_EXACT case (blew a > > changeset some time ago, and finally got around to retesting > > this option). > > > > o Fix some tracing bugs in rcupreempt that caused incorrect > > totals to be printed. > > > > o I now test with a more brutal random-selection online/offline > > script (attached). Probably more brutal than it needs to be > > on the people reading it as well, but so it goes. > > > > o A number of optimizations and usability improvements: > > > > o Make rcu_pending() ignore the grace-period timeout when > > there is no grace period in progress. > > > > o Make force_quiescent_state() avoid going for a global > > lock in the case where there is no grace period in > > progress. > > > > o Rearrange struct fields to improve struct layout. > > > > o Make call_rcu() initiate a grace period if RCU was > > idle, rather than waiting for the next scheduling > > clock interrupt. > > > > o Invoke rcu_irq_enter() and rcu_irq_exit() only when > > idle, as suggested by Andi Kleen. I still don't > > completely trust this change, and might back it out. > > > > o Make CONFIG_RCU_TRACE be the single config variable > > manipulated for all forms of RCU, instead of the prior > > confusion. > > > > o Document tracing files and formats for both rcupreempt > > and rcutree. > > > > Updates from v4 for those missing v5 given its bad subject line: > > > > o Separated dynticks interface so that NMIs and irqs call separate > > functions, greatly simplifying it. In particular, this code > > no longer requires a proof of correctness. ;-) > > > > o Separated dynticks state out into its own per-CPU structure, > > avoiding the duplicated accounting. > > > > o The case where a dynticks-idle CPU runs an irq handler that > > invokes call_rcu() is now correctly handled, forcing that CPU > > out of dynticks-idle mode. > > > > o Review comments have been applied (thank you all!!!). > > For but one example, fixed the dynticks-ordering issue that > > Manfred pointed out, saving me much debugging. ;-) > > > > o Adjusted rcuclassic and rcupreempt to handle dynticks changes. > > > > Attached is an updated patch to Classic RCU that applies a > > hierarchy, greatly reducing the contention on the top-level lock > > for large machines. This passes 10-hour concurrent rcutorture and > > online-offline testing on 128-CPU ppc64 without dynticks enabled, > > and exposes some timekeeping bugs in presence of dynticks (exciting > > working on a system where "sleep 1" hangs until interrupted...). > > It is OK for experimental work, but not yet ready for inclusion. > > See also Manfred Spraul's recent patches (or his earlier work from > > 2004 at http://marc.info/?l=linux-kernel&m=108546384711797&w=2). > > We will converge onto a common patch in the fullness of time, but are > > currently exploring different regions of the design space. That said, > > I have already gratefully stolen quite a few of Manfred's ideas. > > > > This patch provides CONFIG_RCU_FANOUT, which controls the bushiness > > of the RCU hierarchy. Defaults to 32 on 32-bit machines and 64 on > > 64-bit machines. If CONFIG_NR_CPUS is less than CONFIG_RCU_FANOUT, > > there is no hierarchy. By default, the RCU initialization code will > > adjust CONFIG_RCU_FANOUT to balance the hierarchy, so strongly NUMA > > architectures may choose to set CONFIG_RCU_FANOUT_EXACT to disable > > this balancing, allowing the hierarchy to be exactly aligned to the > > underlying hardware. Up to two levels of hierarchy are permitted > > (in addition to the root node), allowing up to 16,384 CPUs on 32-bit > > systems and up to 262,144 CPUs on 64-bit systems. I just know that I > > am going to regret saying this, but this seems more than sufficient > > for the foreseeable future. (Some architectures might wish to set > > CONFIG_RCU_FANOUT=4, which would limit such architectures to 64 CPUs. > > If this becomes a real problem, additional levels can be added, but I > > doubt that it will make a significant difference on real hardware.) > > > > In the common case, a given CPU will manipulate its private rcu_data > > structure and the rcu_node structure that it shares with its immediate > > neighbors. This can reduce both lock and memory contention by multiple > > orders of magnitude, which should eliminate the need for the strange > > manipulations that are reported to be required when running Linux on > > very large systems. > > > > Some shortcomings: > > > > o Some of the NR_CPUS need to be eliminated. That said, some > > will remain. > > > > o There is a bit of debug code in place. This will be removed. > > > > o There are probably hangs, rcutorture failures, &c. Seems > > quite stable on a 128-CPU machine, but that is kind of small > > compared to 4096 CPUs. > > > > o There is not yet a human-readable design document. One is now > > close to completion. > > > > Credits: > > > > o Manfred Spraul for ideas, review comments, and bugs spotted, > > as well as some good friendly competition. ;-) > > > > o Josh Triplett, Ingo Molnar, Peter Zijlstra, Mathieu Desnoyers, > > Lai Jiangshan, Andi Kleen, Andy Whitcroft, and Andrew Morton > > for reviews and comments. > > > > o Thomas Gleixner for much-needed help with some timer issues > > (see patches below). > > > > o Jon M. Tollefson, Tim Pepper, Andrew Theurer, Jose R. Santos, > > Andy Whitcroft, Darrick Wong, Nishanth Aravamudan, Anton > > Blanchard, and Nathan Lynch for keeping machines alive despite > > my heavy abuse^Wtesting. > > > > To build, start with 2.6.27-rc7, and apply: > > > > http://www.rdrop.com/users/paulmck/patches/2.6.27-rc3-treeRCU-20.patch > > http://tglx.de/~tglx/gack.patch > > http://tglx.de/~tglx/clockevents-keep-tick-next-period-up-to-date.patch > > > > Thoughts? > > > > > Signed-off-by: Paul E. McKenney > > --- > > > > Documentation/RCU/00-INDEX | 2 > > Documentation/RCU/trace.txt | 398 ++++++++ > > arch/powerpc/platforms/pseries/rtasd.c | 4 > > include/linux/hardirq.h | 14 > > include/linux/rcupdate.h | 10 > > include/linux/rcutree.h | 325 +++++++ > > init/Kconfig | 18 > > kernel/Kconfig.preempt | 62 + > > kernel/Makefile | 6 > > kernel/rcupreempt.c | 10 > > kernel/rcupreempt_trace.c | 10 > > kernel/rcutree.c | 1510 +++++++++++++++++++++++++++++++++ > > kernel/rcutree_trace.c | 232 +++++ > > kernel/softirq.c | 15 > > lib/Kconfig.debug | 13 > > 15 files changed, 2595 insertions(+), 34 deletions(-) > > > > diff --git a/Documentation/RCU/00-INDEX b/Documentation/RCU/00-INDEX > > index 461481d..7dc0695 100644 > > --- a/Documentation/RCU/00-INDEX > > +++ b/Documentation/RCU/00-INDEX > > @@ -16,6 +16,8 @@ RTFP.txt > > - List of RCU papers (bibliography) going back to 1980. > > torture.txt > > - RCU Torture Test Operation (CONFIG_RCU_TORTURE_TEST) > > +trace.txt > > + - CONFIG_RCU_TRACE debugfs files and formats > > UP.txt > > - RCU on Uniprocessor Systems > > whatisRCU.txt > > diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt > > new file mode 100644 > > index 0000000..d25110c > > --- /dev/null > > +++ b/Documentation/RCU/trace.txt > > @@ -0,0 +1,398 @@ > > +CONFIG_RCU_TRACE debugfs Files and Formats > > + > > + > > +The rcupreempt and rcutree implementations of RCU provide debugfs trace > > +output that summarizes counters and state. This information is useful for > > +debugging RCU itself, and can sometimes also help to debug abuses of RCU. > > +Note that the rcuclassic implementation of RCU does not provide debugfs > > +trace output. > > + > > +The following sections describe the debugfs files and formats for > > +preemptable RCU (rcupreempt) and hierarchical RCU (rcutree). > > + > > + > > +Preemptable RCU debugfs Files and Formats > > + > > +This implementation of RCU provides three debugfs files under the > > +top-level directory RCU: rcu/rcuctrs (which displays the per-CPU > > +counters used by preemptable RCU) rcu/rcugp (which displays grace-period > > +counters), and rcu/rcustats (which internal counters for debugging RCU). > > + > > +The output of "cat rcu/rcuctrs" looks as follows: > > + > > +CPU last cur F M > > + 0 5 -5 0 0 > > + 1 -1 0 0 0 > > + 2 0 1 0 0 > > + 3 0 1 0 0 > > + 4 0 1 0 0 > > + 5 0 1 0 0 > > + 6 0 2 0 0 > > + 7 0 -1 0 0 > > + 8 0 1 0 0 > > +ggp = 26226, state = waitzero > > + > > +The per-CPU fields are as follows: > > + > > +o "CPU" gives the CPU number. Offline CPUs are not displayed. > > + > > +o "last" gives the value of the counter that is being decremented > > + for the current grace period phase. In the example above, > > + the counters sum to 4, indicating that there are still four > > + RCU read-side critical sections still running that started > > + before the last counter flip. > > + > > +o "cur" gives the value of the counter that is currently being > > + both incremented (by rcu_read_lock()) and decremented (by > > + rcu_read_unlock()). In the example above, the counters sum to > > + 1, indicating that there is only one RCU read-side critical section > > + still running that started after the last counter flip. > > + > > +o "F" indicates whether RCU is waiting for this CPU to acknowledge > > + a counter flip. In the above example, RCU is not waiting on any, > > + which is consistent with the state being "waitzero" rather than > > + "waitack". > > + > > +o "M" indicates whether RCU is waiting for this CPU to execute a > > + memory barrier. In the above example, RCU is not waiting on any, > > + which is consistent with the state being "waitzero" rather than > > + "waitmb". > > + > > +o "ggp" is the global grace-period counter. > > + > > +o "state" is the RCU state, which can be one of the following: > > + > > + o "idle": there is no grace period in progress. > > + > > + o "waitack": RCU just incremented the global grace-period > > + counter, which has the effect of reversing the roles of > > + the "last" and "cur" counters above, and is waiting for > > + all the CPUs to acknowledge the flip. Once the flip has > > + been acknowledged, CPUs will no longer be incrementing > > + what are now the "last" counters, so that their sum will > > + decrease monotonically down to zero. > > + > > + o "waitzero": RCU is waiting for the sum of the "last" counters > > + to decrease to zero. > > + > > + o "waitmb": RCU is waiting for each CPU to execute a memory > > + barrier, which ensures that instructions from a given CPU's > > + last RCU read-side critical section cannot be reordered > > + with instructions following the memory-barrier instruction. > > + > > +The output of "cat rcu/rcugp" looks as follows: > > + > > +oldggp=48870 newggp=48873 > > + > > +Note that reading from this file provokes a synchronize_rcu(). The > > +"oldggp" value is that of "ggp" from rcu/rcuctrs above, taken before > > +executing the synchronize_rcu(), and the "newggp" value is also the > > +"ggp" value, but taken after the synchronize_rcu() command returns. > > + > > + > > +The output of "cat rcu/rcugp" looks as follows: > > + > > +na=1337955 nl=40 wa=1337915 wl=44 da=1337871 dl=0 dr=1337871 di=1337871 > > +1=50989 e1=6138 i1=49722 ie1=82 g1=49640 a1=315203 ae1=265563 a2=49640 > > +z1=1401244 ze1=1351605 z2=49639 m1=5661253 me1=5611614 m2=49639 > > + > > +These are counters tracking internal preemptable-RCU events, however, > > +some of them may be useful for debugging algorithms using RCU. In > > +particular, the "nl", "wl", and "dl" values track the number of RCU > > +callbacks in various states. The fields are as follows: > > + > > +o "na" is the total number of RCU callbacks that have been enqueued > > + since boot. > > + > > +o "nl" is the number of RCU callbacks waiting for the previous > > + grace period to end so that they can start waiting on the next > > + grace period. > > + > > +o "wa" is the total number of RCU callbacks that have started waiting > > + for a grace period since boot. "na" should be roughly equal to > > + "nl" plus "wa". > > + > > +o "wl" is the number of RCU callbacks currently waiting for their > > + grace period to end. > > + > > +o "da" is the total number of RCU callbacks whose grace periods > > + have completed since boot. "wa" should be roughly equal to > > + "wl" plus "da". > > + > > +o "dr" is the total number of RCU callbacks that have been removed > > + from the list of callbacks ready to invoke. "dr" should be roughly > > + equal to "da". > > + > > +o "di" is the total number of RCU callbacks that have been invoked > > + since boot. "di" should be roughly equal to "da", though some > > + early versions of preemptable RCU had a bug so that only the > > + last CPU's count of invocations was displayed, rather than the > > + sum of all CPU's counts. > > + > > +o "1" is the number of calls to rcu_try_flip(). This should be > > + roughly equal to the sum of "e1", "i1", "a1", "z1", and "m1" > > + described below. In other words, the number of times that > > + the state machine is visited should be equal to the sum of the > > + number of times that each state is visited plus the number of > > + times that the state-machine lock acquisition failed. > > + > > +o "e1" is the number of times that rcu_try_flip() was unable to > > + acquire the fliplock. > > + > > +o "i1" is the number of calls to rcu_try_flip_idle(). > > + > > +o "ie1" is the number of times rcu_try_flip_idle() exited early > > + due to the calling CPU having no work for RCU. > > + > > +o "g1" is the number of times that rcu_try_flip_idle() decided > > + to start a new grace period. "i1" should be roughly equal to > > + "ie1" plus "g1". > > + > > +o "a1" is the number of calls to rcu_try_flip_waitack(). > > + > > +o "ae1" is the number of times that rcu_try_flip_waitack() found > > + that at least one CPU had not yet acknowledge the new grace period > > + (AKA "counter flip"). > > + > > +o "a2" is the number of time rcu_try_flip_waitack() found that > > + all CPUs had acknowledged. "a1" should be roughly equal to > > + "ae1" plus "a2". (This particular output was collected on > > + a 128-CPU machine, hence the smaller-than-usual fraction of > > + calls to rcu_try_flip_waitack() finding all CPUs having already > > + acknowledged.) > > + > > +o "z1" is the number of calls to rcu_try_flip_waitzero(). > > + > > +o "ze1" is the number of times that rcu_try_flip_waitzero() found > > + that not all of the old RCU read-side critical sections had > > + completed. > > + > > +o "z2" is the number of times that rcu_try_flip_waitzero() finds > > + the sum of the counters equal to zero, in other words, that > > + all of the old RCU read-side critical sections had completed. > > + The value of "z1" should be roughly equal to "ze1" plus > > + "z2". > > + > > +o "m1" is the number of calls to rcu_try_flip_waitmb(). > > + > > +o "me1" is the number of times that rcu_try_flip_waitmb() finds > > + that at least one CPU has not yet executed a memory barrier. > > + > > +o "m2" is the number of times that rcu_try_flip_waitmb() finds that > > + all CPUs have executed a memory barrier. > > + > > + > > +Hierarchical RCU debugfs Files and Formats > > + > > +This implementation of RCU provides three debugfs files under the > > +top-level directory RCU: rcu/rcudata (which displays fields in struct > > +rcu_data), rcu/rcugp (which displays grace-period counters), and > > +rcu/rcuhier (which displays the struct rcu_node hierarchy). > > + > > +The output of "cat rcu/rcudata" looks as follows: > > + > > +rcu: > > + 0 c=1985 g=1986 pq=1 pqc=1985 qp=0 dt=26097 dn=2 df=9102 of=0 ri=11 ql=2 b=10 > > + 1 c=1985 g=1986 pq=1 pqc=1985 qp=0 dt=30421 dn=2 df=6608 of=0 ri=2 ql=39 b=10 > > + 2 c=1982 g=1982 pq=1 pqc=1982 qp=0 dt=10934 dn=2 df=9612 of=0 ri=0 ql=0 b=10 > > + 3 c=1985 g=1986 pq=1 pqc=1985 qp=0 dt=30139 dn=2 df=6043 of=0 ri=0 ql=58 b=10 > > + 4 c=1960 g=1960 pq=1 pqc=1960 qp=1 dt=1202 dn=2 df=30470 of=0 ri=3 ql=0 b=10 > > + 5 c=1985 g=1986 pq=1 pqc=1985 qp=0 dt=15341 dn=2 df=5350 of=0 ri=0 ql=25 b=10 > > + 6 c=1983 g=1984 pq=1 pqc=1983 qp=1 dt=516 dn=2 df=31950 of=0 ri=0 ql=0 b=10 > > + 7 c=1985 g=1986 pq=1 pqc=1985 qp=0 dt=8205 dn=2 df=7465 of=0 ri=0 ql=28 b=10 > > +rcu_bh: > > + 0 c=375 g=375 pq=1 pqc=375 qp=0 dt=26097 dn=2 df=0 of=0 ri=0 ql=0 b=10 > > + 1 c=375 g=375 pq=1 pqc=375 qp=0 dt=30421 dn=2 df=162 of=0 ri=0 ql=0 b=10 > > + 2 c=375 g=375 pq=1 pqc=375 qp=1 dt=10934 dn=2 df=162 of=0 ri=0 ql=0 b=10 > > + 3 c=375 g=375 pq=1 pqc=375 qp=0 dt=30139 dn=2 df=107 of=0 ri=0 ql=0 b=10 > > + 4 c=375 g=375 pq=1 pqc=375 qp=1 dt=1202 dn=2 df=174 of=0 ri=0 ql=0 b=10 > > + 5 c=375 g=375 pq=1 pqc=375 qp=0 dt=15341 dn=2 df=122 of=0 ri=0 ql=0 b=10 > > + 6 c=375 g=375 pq=1 pqc=375 qp=1 dt=516 dn=2 df=117 of=0 ri=0 ql=0 b=10 > > + 7 c=375 g=375 pq=1 pqc=375 qp=0 dt=8205 dn=2 df=127 of=0 ri=0 ql=0 b=10 > > + > > +The first section lists the rcu_data structures for rcu, the second for > > +rcu_bh. Each section has one line per CPU, or eight for this 8-CPU system. > > +The fields are as follows: > > + > > +o The number at the beginning of each line is the CPU number. > > + CPUs numbers followed by an exclamation mark are offline, > > + but have been online at least once since boot. There will be > > + no output for CPUs that have never been online, which can be > > + a good thing in the surprisingly common case where NR_CPUS is > > + substantially larger than the number of actual CPUs. > > + > > +o "c" is the count of grace periods that this CPU believes have > > + completed. CPUs in dynticks idle mode may lag quite a ways > > + behind, for example, CPU 4 under "rcu" above, which has slept > > + through the past 25 RCU grace periods. It is not unusual to > > + see CPUs lagging by thousands of grace periods. > > + > > +o "g" is the count of grace periods that this CPU believes have > > + started. Again, CPUs in dynticks idle mode may lag behind. > > + If the "c" and "g" values are equal, this CPU has already > > + reported a quiescent state for the last RCU grace period that > > + it is aware of, otherwise, the CPU believes that it owes RCU a > > + quiescent state. > > + > > +o "pq" indicates that this CPU has passed through a quiescent state > > + for the current grace period. It is possible for "pq" to be > > + "1" and "c" different than "g", which indicates that although > > + the CPU has passed through a quiescent state, either (1) this > > + CPU has not yet reported that fact, (2) some other CPU has not > > + yet reported for this grace period, or (3) both. > > + > > +o "pqc" indicates which grace period the last-observed quiescent > > + state for this CPU corresponds to. This is important for handling > > + the race between CPU 0 reporting an extended dynticks-idle > > + quiescent state for CPU 1 and CPU 1 suddenly waking up and > > + reporting its own quiescent state. If CPU 1 was the last CPU > > + for the current grace period, then the CPU that loses this race > > + will attempt to incorrectly mark CPU 1 as having checked in for > > + the next grace period! > > + > > +o "qp" indicates that RCU still expects a quiescent state from > > + this CPU. > > + > > +o "dt" is the current value of the dyntick counter that is incremented > > + when entering or leaving dynticks idle state, either by the > > + scheduler or by irq. > > + > > + This field is displayed only for CONFIG_NO_HZ kernels. > > + > > +o "dn" is the current value of the dyntick counter that is incremented > > + when entering or leaving dynticks idle state via NMI. If both > > + the "dt" and "dn" values are even, then this CPU is in dynticks > > + idle mode and may be ignored by RCU. If either of these two > > + counters is odd, then RCU must be alert to the possibility of > > + an RCU read-side critical section running on this CPU. > > + > > + This field is displayed only for CONFIG_NO_HZ kernels. > > + > > +o "df" is the number of times that some other CPU has forced a > > + quiescent state on behalf of this CPU due to this CPU being in > > + dynticks-idle state. > > + > > + This field is displayed only for CONFIG_NO_HZ kernels. > > + > > +o "of" is the number of times that some other CPU has forced a > > + quiescent state on behalf of this CPU due to this CPU being > > + offline. In a perfect world, this might neve happen, but it > > + turns out that offlining and onlining a CPU can take several grace > > + periods, and so there is likely to be an extended period of time > > + when RCU believes that the CPU is online when it really is not. > > + Please note that erring in the other direction (RCU believing a > > + CPU is offline when it is really alive and kicking) is a fatal > > + error, so it makes sense to err conservatively. > > + > > +o "ri" is the number of times that RCU has seen fit to send a > > + reschedule IPI to this CPU in order to get it to report a > > + quiescent state. > > + > > +o "ql" is the number of RCU callbacks currently residing on > > + this CPU. This is the total number of callbacks, regardless > > + of what state they are in (new, waiting for grace period to > > + start, waiting for grace period to end, ready to invoke). > > + > > +o "b" is the batch limit for this CPU. If more than this number > > + of RCU callbacks is ready to invoke, then the remainder will > > + be deferred. > > + > > + > > +The output of "cat rcu/rcudata" looks as follows: > > + > > +rcu: completed=33062 gpnum=33063 > > +rcu_bh: completed=464 gpnum=464 > > + > > +Again, this output is for both "rcu" and "rcu_bh". The fields are > > +taken from the rcu_state structure, and are as follows: > > + > > +o "completed" is the number of grace periods that have completed. > > + It is comparable to the "c" field from rcu/rcudata in that a > > + CPU whose "c" field matches the value of "completed" is aware > > + that the corresponding RCU grace period has completed. > > + > > +o "gpnum" is the number of grace periods that have started. It is > > + comparable to the "g" field from rcu/rcudata in that a CPU > > + whose "g" field matches the value of "gpnum" is aware that the > > + corresponding RCU grace period has started. > > + > > + If these two fields are equal (as they are for "rcu_bh" above), > > + then there is no grace period in progress, in other words, RCU > > + is idle. On the other hand, if the two fields differ (as they > > + do for "rcu" above), then an RCU grace period is in progress. > > + > > + > > +The output of "cat rcu/rcuhier" looks as follows, with very long lines: > > + > > +rcu: > > +c=33184 g=33185 s=0 jfq=1 nfqs=61601/nfqsng=28011(33590) > > +1/1 0:127 ^0 > > +1/3 0:35 ^0 0/0 36:71 ^1 0/0 72:107 ^2 0/0 108:127 ^3 > > +14/3f 0:5 ^0 0/3 6:11 ^1 0/0 12:17 ^2 0/0 18:23 ^3 0/0 24:29 ^4 0/0 30:35 ^5 0/0 36:41 ^0 0/0 42:47 ^1 0/0 48:53 ^2 0/0 54:59 ^3 0/0 60:65 ^4 0/0 66:71 ^5 0/0 72:77 ^0 0/0 78:83 ^1 0/0 84:89 ^2 0/0 90:95 ^3 0/0 96:101 ^4 0/0 102:107 ^5 0/0 108:113 ^0 0/0 114:119 ^1 0/0 120:125 ^2 0/0 126:127 ^3 > > +rcu_bh: > > +c=470 g=470 s=0 jfq=2 nfqs=62302/nfqsng=62027(275) > > +0/1 0:127 ^0 > > +0/3 0:35 ^0 0/0 36:71 ^1 0/0 72:107 ^2 0/0 108:127 ^3 > > +0/3f 0:5 ^0 0/3 6:11 ^1 0/0 12:17 ^2 0/0 18:23 ^3 0/0 24:29 ^4 0/0 30:35 ^5 0/0 36:41 ^0 0/0 42:47 ^1 0/0 48:53 ^2 0/0 54:59 ^3 0/0 60:65 ^4 0/0 66:71 ^5 0/0 72:77 ^0 0/0 78:83 ^1 0/0 84:89 ^2 0/0 90:95 ^3 0/0 96:101 ^4 0/0 102:107 ^5 0/0 108:113 ^0 0/0 114:119 ^1 0/0 120:125 ^2 0/0 126:127 ^3 > > + > > +This is once again split into "rcu" and "rcu_bh" portions. The fields are > > +as follows: > > + > > +o "c" is exactly the same as "completed" under rcu/rcugp. > > + > > +o "g" is exactly the same as "gpnum" under rcu/rcugp. > > + > > +o "s" is the "signaled" state that drives force_quiescent_state()'s > > + state machine. > > + > > +o "jfq" is the number of jiffies remaining for this grace period > > + before force_quiescent_state() is invoked to help push things > > + along. Note that CPUs in dyntick-idle mode thoughout the grace > > + period will not report on their own, but rather must be check by > > + some other CPU via force_quiescent_state(). > > + > > +o "nfqs" is the number of calls to force_quiescent_state() since > > + boot. > > + > > +o "nfqsng" is the number of useless calls to force_quiescent_state(), > > + where there wasn't actually a grace period active. This can > > + happen due to races. The number in parentheses is the difference > > + between "nfqs" and "nfqsng", or the number of times that > > + force_quiescent_state() actually did some real work. > > + > > +o Each element of the form "1/1 0:127 ^0" represents one struct > > + rcu_node. Each line represents one level of the hierarchy, from > > + root to leaves. It is best to think of the rcu_data structures > > + as forming yet another level after the leaves. Note that there > > + might be either one, two, or three levels of rcu_node structures, > > + depending on the relationship between CONFIG_RCU_FANOUT and > > + CONFIG_NR_CPUS. > > + > > + o The numbers separated by the "/" are the qsmask followed > > + by the qsmaskinit. The qsmask will have one bit > > + set for each entity in the next lower level that > > + has not yet checked in for the current grace period. > > + The qsmaskinit will have one bit for each entity that is > > + currently expected to check in during each grace period. > > + The value of qsmaskinit is assigned to that of qsmask > > + at the beginning of each grace period. > > + > > + For example, for "rcu", the qsmask of the first entry > > + of the lowest level is 0x14, meaning that we are still > > + waiting for CPUs 2 and 4 to check in for the current > > + grace period. > > + > > + o The numbers separated by the ":" are the range of CPUs > > + served by this struct rcu_node. This can be helpful > > + in working out how the hierarchy is wired together. > > + > > + For example, the first entry at the lowest level shows > > + "0:5", indicating that it covers CPUs 0 through 5. > > + > > + o The number after the "^" indicates the bit in the > > + next higher level rcu_node structure that this > > + rcu_node structure corresponds to. > > + > > + For example, the first entry at the lowest level shows > > + "^0", indicating that it corresponds to bit zero in > > + the first entry at the middle level. > > diff --git a/arch/powerpc/platforms/pseries/rtasd.c b/arch/powerpc/platforms/pseries/rtasd.c > > index c9ffd8c..d8e784a 100644 > > --- a/arch/powerpc/platforms/pseries/rtasd.c > > +++ b/arch/powerpc/platforms/pseries/rtasd.c > > @@ -208,6 +208,7 @@ void pSeries_log_error(char *buf, unsigned int err_type, int fatal) > > break; > > case ERR_TYPE_KERNEL_PANIC: > > default: > > + WARN_ON_ONCE(!irqs_disabled()); /* @@@ DEBUG @@@ */ > > spin_unlock_irqrestore(&rtasd_log_lock, s); > > return; > > } > > @@ -227,6 +228,7 @@ void pSeries_log_error(char *buf, unsigned int err_type, int fatal) > > /* Check to see if we need to or have stopped logging */ > > if (fatal || !logging_enabled) { > > logging_enabled = 0; > > + WARN_ON_ONCE(!irqs_disabled()); /* @@@ DEBUG @@@ */ > > spin_unlock_irqrestore(&rtasd_log_lock, s); > > return; > > } > > @@ -249,11 +251,13 @@ void pSeries_log_error(char *buf, unsigned int err_type, int fatal) > > else > > rtas_log_start += 1; > > > > + WARN_ON_ONCE(!irqs_disabled()); /* @@@ DEBUG @@@ */ > > spin_unlock_irqrestore(&rtasd_log_lock, s); > > wake_up_interruptible(&rtas_log_wait); > > break; > > case ERR_TYPE_KERNEL_PANIC: > > default: > > + WARN_ON_ONCE(!irqs_disabled()); /* @@@ DEBUG @@@ */ > > spin_unlock_irqrestore(&rtasd_log_lock, s); > > return; > > } > > diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h > > index 181006c..9b70b92 100644 > > --- a/include/linux/hardirq.h > > +++ b/include/linux/hardirq.h > > @@ -118,13 +118,17 @@ static inline void account_system_vtime(struct task_struct *tsk) > > } > > #endif > > > > -#if defined(CONFIG_PREEMPT_RCU) && defined(CONFIG_NO_HZ) > > +#if defined(CONFIG_NO_HZ) && !defined(CONFIG_CLASSIC_RCU) > > extern void rcu_irq_enter(void); > > extern void rcu_irq_exit(void); > > +extern void rcu_nmi_enter(void); > > +extern void rcu_nmi_exit(void); > > #else > > # define rcu_irq_enter() do { } while (0) > > # define rcu_irq_exit() do { } while (0) > > -#endif /* CONFIG_PREEMPT_RCU */ > > +# define rcu_nmi_enter() do { } while (0) > > +# define rcu_nmi_exit() do { } while (0) > > +#endif /* #if defined(CONFIG_NO_HZ) && !defined(CONFIG_CLASSIC_RCU) */ > > > > /* > > * It is safe to do non-atomic ops on ->hardirq_context, > > @@ -134,7 +138,6 @@ extern void rcu_irq_exit(void); > > */ > > #define __irq_enter() \ > > do { \ > > - rcu_irq_enter(); \ > > account_system_vtime(current); \ > > add_preempt_count(HARDIRQ_OFFSET); \ > > trace_hardirq_enter(); \ > > @@ -153,7 +156,6 @@ extern void irq_enter(void); > > trace_hardirq_exit(); \ > > account_system_vtime(current); \ > > sub_preempt_count(HARDIRQ_OFFSET); \ > > - rcu_irq_exit(); \ > > } while (0) > > > > /* > > @@ -161,7 +163,7 @@ extern void irq_enter(void); > > */ > > extern void irq_exit(void); > > > > -#define nmi_enter() do { lockdep_off(); __irq_enter(); } while (0) > > -#define nmi_exit() do { __irq_exit(); lockdep_on(); } while (0) > > +#define nmi_enter() do { lockdep_off(); rcu_nmi_enter(); __irq_enter(); } while (0) > > +#define nmi_exit() do { __irq_exit(); rcu_nmi_exit(); lockdep_on(); } while (0) > > > > #endif /* LINUX_HARDIRQ_H */ > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index e8b4039..f8544ae 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -52,11 +52,15 @@ struct rcu_head { > > void (*func)(struct rcu_head *head); > > }; > > > > -#ifdef CONFIG_CLASSIC_RCU > > +#if defined(CONFIG_CLASSIC_RCU) > > #include > > -#else /* #ifdef CONFIG_CLASSIC_RCU */ > > +#elif defined(CONFIG_TREE_RCU) > > +#include > > +#elif defined(CONFIG_PREEMPT_RCU) > > #include > > -#endif /* #else #ifdef CONFIG_CLASSIC_RCU */ > > +#else > > +#error "Unknown RCU implementation specified to kernel configuration" > > +#endif /* #else #if defined(CONFIG_CLASSIC_RCU) */ > > > > #define RCU_HEAD_INIT { .next = NULL, .func = NULL } > > #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT > > diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h > > new file mode 100644 > > index 0000000..00f8be2 > > --- /dev/null > > +++ b/include/linux/rcutree.h > > @@ -0,0 +1,325 @@ > > +/* > > + * Read-Copy Update mechanism for mutual exclusion (tree-based version) > > + * > > + * This program is free software; you can redistribute it and/or modify > > + * it under the terms of the GNU General Public License as published by > > + * the Free Software Foundation; either version 2 of the License, or > > + * (at your option) any later version. > > + * > > + * This program is distributed in the hope that it will be useful, > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > + * GNU General Public License for more details. > > + * > > + * You should have received a copy of the GNU General Public License > > + * along with this program; if not, write to the Free Software > > + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. > > + * > > + * Copyright IBM Corporation, 2008 > > + * > > + * Author: Dipankar Sarma > > + * Paul E. McKenney Hierarchical algorithm > > + * > > + * Based on the original work by Paul McKenney > > + * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. > > + * > > + * For detailed explanation of Read-Copy Update mechanism see - > > + * Documentation/RCU > > + */ > > + > > +#ifndef __LINUX_RCUTREE_H > > +#define __LINUX_RCUTREE_H > > + > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +/* > > + * Define shape of hierarchy based on NR_CPUS and CONFIG_RCU_FANOUT. > > + * In theory, it should be possible to add more levels straightforwardly. > > + * In practice, this has not been tested, so there is probably some > > + * bug somewhere. > > + */ > > +#define MAX_RCU_LVLS 3 > > +#define RCU_FANOUT (CONFIG_RCU_FANOUT) > > +#define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT) > > +#define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT) > > + > > +#if (NR_CPUS) <= RCU_FANOUT > > +# define NUM_RCU_LVLS 1 > > +# define NUM_RCU_LVL_0 1 > > +# define NUM_RCU_LVL_1 (NR_CPUS) > > +# define NUM_RCU_LVL_2 0 > > +# define NUM_RCU_LVL_3 0 > > +#elif (NR_CPUS) <= RCU_FANOUT_SQ > > +# define NUM_RCU_LVLS 2 > > +# define NUM_RCU_LVL_0 1 > > +# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT) > > +# define NUM_RCU_LVL_2 (NR_CPUS) > > +# define NUM_RCU_LVL_3 0 > > +#elif (NR_CPUS) <= RCU_FANOUT_CUBE > > +# define NUM_RCU_LVLS 3 > > +# define NUM_RCU_LVL_0 1 > > +# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ) > > +# define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT)) > > +# define NUM_RCU_LVL_3 NR_CPUS > > +#else > > +# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS" > > +#endif /* #if (NR_CPUS) <= RCU_FANOUT */ > > + > > +#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3) > > +#define NUM_RCU_NODES (RCU_SUM - NR_CPUS) > > + > > +/* > > + * Dynticks per-CPU state. > > + */ > > +struct rcu_dynticks { > > + int dynticks_nesting; /* Track nesting level, sort of. */ > > + int dynticks; /* Even value for dynticks-idle, else odd. */ > > + int dynticks_nmi; /* Even value for either dynticks-idle or */ > > + /* not in nmi handler, else odd. So this */ > > + /* remains even for nmi from irq handler. */ > > +}; > > + > > +/* > > + * Definition for node within the RCU grace-period-detection hierarchy. > > + */ > > +struct rcu_node { > > + spinlock_t lock; > > + unsigned long qsmask; /* CPUs or groups that need to switch in */ > > + /* order for current grace period to proceed.*/ > > + unsigned long qsmaskinit; > > + /* Per-GP initialization for qsmask. */ > > + unsigned long grpmask; /* Mask to apply to parent qsmask. */ > > + int grplo; /* lowest-numbered CPU or group here. */ > > + int grphi; /* highest-numbered CPU or group here. */ > > + u8 grpnum; /* CPU/group number for next level up. */ > > + u8 level; /* root is at level 0. */ > > + struct rcu_node *parent; > > +} ____cacheline_internodealigned_in_smp; > > + > > +/* Index values for nxttail array in struct rcu_data. */ > > +#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */ > > +#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */ > > +#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */ > > +#define RCU_NEXT_TAIL 3 > > +#define RCU_NEXT_SIZE 4 > > + > > +/* Per-CPU data for read-copy update. */ > > +struct rcu_data { > > + /* 1) quiescent-state and grace-period handling : */ > > + long completed; /* Track rsp->completed gp number */ > > + /* in order to detect GP end. */ > > + long gpnum; /* Highest gp number that this CPU */ > > + /* is aware of having started. */ > > + long passed_quiesc_completed; > > + /* Value of completed at time of qs. */ > > + bool passed_quiesc; /* User-mode/idle loop etc. */ > > + bool qs_pending; /* Core waits for quiesc state. */ > > + bool beenonline; /* CPU online at least once. */ > > + struct rcu_node *mynode; /* This CPU's leaf of hierarchy */ > > + unsigned long grpmask; /* Mask to apply to leaf qsmask. */ > > + > > + /* 2) batch handling */ > > + /* > > + * If nxtlist is not NULL, it is partitioned as follows. > > + * Any of the partitions might be empty, in which case the > > + * pointer to that partition will be equal to the pointer for > > + * the following partition. When the list is empty, all of > > + * the nxttail elements point to nxtlist, which is NULL. > > + * > > + * [*nxttail[RCU_NEXT_READY_TAIL], NULL = *nxttail[RCU_NEXT_TAIL]): > > + * Entries that might have arrived after current GP ended > > + * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]): > > + * Entries known to have arrived before current GP ended > > + * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]): > > + * Entries that batch # <= ->completed - 1: waiting for current GP > > + * [nxtlist, *nxttail[RCU_DONE_TAIL]): > > + * Entries that batch # <= ->completed > > + * The grace period for these entries has completed, and > > + * the other grace-period-completed entries may be moved > > + * here temporarily in rcu_process_callbacks(). > > + */ > > + struct rcu_head *nxtlist; > > + struct rcu_head **nxttail[RCU_NEXT_SIZE]; > > + long qlen; /* # of queued callbacks */ > > + long blimit; /* Upper limit on a processed batch */ > > + > > + /* 3) rcu-barrier functions */ > > + struct rcu_head barrier; > > + > > +#ifdef CONFIG_NO_HZ > > + /* 4) dynticks interface (see http://lwn.net/Articles/279077/) */ > > + struct rcu_dynticks *dynticks; /* Shared per-CPU dynticks state. */ > > + int dynticks_snap; /* Per-GP tracking for dynticks. */ > > + int dynticks_nmi_snap; /* Per-GP tracking for dynticks_nmi. */ > > +#endif /* #ifdef CONFIG_NO_HZ */ > > + > > + /* 5) reasons this CPU needed to be kicked by force_quiescent_state */ > > +#ifdef CONFIG_NO_HZ > > + unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */ > > +#endif /* #ifdef CONFIG_NO_HZ */ > > + unsigned long offline_fqs; /* Kicked due to being offline. */ > > + unsigned long resched_ipi; /* Sent a resched IPI. */ > > + > > + int cpu; > > +}; > > + > > +/* Values for signaled field in struc rcu_data. */ > ^^^^^^^^^^^^^^^^^^ > => should be struct rcu_state. Fixed! > > +#define RCU_SAVE_DYNTICK 0 /* Need to scan dyntick state. */ > > +#define RCU_FORCE_QS 1 /* Need to force quiescent state. */ > > +#ifdef CONFIG_NO_HZ > > +#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK > > +#else /* #ifdef CONFIG_NO_HZ */ > > +#define RCU_SIGNAL_INIT RCU_FORCE_QS > > +#endif /* #else #ifdef CONFIG_NO_HZ */ > > + > > +#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */ > > +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR > > +#define RCU_SECONDS_TILL_STALL_CHECK (3 * HZ) /* for rsp->jiffies_stall */ > > +#define RCU_SECONDS_TILL_STALL_RECHECK (30 * HZ) /* for rsp->jiffies_stall */ > > +#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */ > > + /* to take at least one */ > > + /* scheduling clock irq */ > > + /* before ratting on them. */ > > + > > +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ > > + > > +/* > > + * RCU global state, including node hierarchy. This hierarchy is > > + * represented in "heap" form in a dense array. The root (first level) > > + * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second > > + * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]), > > + * and the third level in ->node[m+1] and following (->node[m+1] referenced > > + * by ->level[2]). The number of levels is determined by the number of > > + * CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy" > > + * consisting of a single rcu_node. > > + */ > > +struct rcu_state { > > + struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */ > > + struct rcu_node *level[NUM_RCU_LVLS]; /* Hierarchy levels. */ > > + u32 levelcnt[MAX_RCU_LVLS + 1]; /* # nodes in each level. */ > > + u8 levelspread[NUM_RCU_LVLS]; /* kids/node in each level. */ > > + struct rcu_data *rda[NR_CPUS]; /* array of rdp pointers. */ > > + > > + /* The following fields are guarded by the root rcu_node's lock. */ > > + > > + u8 signaled ____cacheline_internodealigned_in_smp; > > + /* Force QS state. */ > > + long gpnum; /* Current gp number. */ > > + long completed; /* # of last completed gp. */ > > + spinlock_t onofflock; /* exclude on/offline and */ > > + /* starting new GP. */ > > + spinlock_t fqslock; /* Only one task forcing */ > > + /* quiescent states. */ > > + unsigned long jiffies_force_qs; /* Time at which to invoke */ > > + /* force_quiescent_state(). */ > > + unsigned long n_force_qs; /* Number of calls to */ > > + /* force_quiescent_state(). */ > > + unsigned long n_force_qs_ngp; /* Number of calls leaving */ > > + /* due to no GP active. */ > > +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR > > + unsigned long gp_start; /* Time at which GP started, */ > > + /* but in jiffies. */ > > + unsigned long jiffies_stall; /* Time at which to check */ > > + /* for CPU stalls. */ > > +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ > > +#ifdef CONFIG_NO_HZ > > + long dynticks_completed; /* Value of completed @ snap. */ > > +#endif /* #ifdef CONFIG_NO_HZ */ > > +}; > > + > > +extern struct rcu_state rcu_state; > > +DECLARE_PER_CPU(struct rcu_data, rcu_data); > > + > > +extern struct rcu_state rcu_bh_state; > > +DECLARE_PER_CPU(struct rcu_data, rcu_bh_data); > > + > > +/* > > + * Increment the quiescent state counter. > > + * The counter is a bit degenerated: We do not need to know > > + * how many quiescent states passed, just if there was at least > > + * one since the start of the grace period. Thus just a flag. > > + */ > > +static inline void rcu_qsctr_inc(int cpu) > > +{ > > + struct rcu_data *rdp = &per_cpu(rcu_data, cpu); > > + rdp->passed_quiesc = 1; > > + rdp->passed_quiesc_completed = rdp->completed; > > +} > > +static inline void rcu_bh_qsctr_inc(int cpu) > > +{ > > + struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); > > + rdp->passed_quiesc = 1; > > + rdp->passed_quiesc_completed = rdp->completed; > > +} > > + > > +extern int rcu_pending(int cpu); > > +extern int rcu_needs_cpu(int cpu); > > + > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > > +extern struct lockdep_map rcu_lock_map; > > +# define rcu_read_acquire() \ > > + lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_) > > +# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) > > +#else > > +# define rcu_read_acquire() do { } while (0) > > +# define rcu_read_release() do { } while (0) > > +#endif > > + > > +static inline void __rcu_read_lock(void) > > +{ > > + preempt_disable(); > > + __acquire(RCU); > > + rcu_read_acquire(); > > +} > > +static inline void __rcu_read_unlock(void) > > +{ > > + rcu_read_release(); > > + __release(RCU); > > + preempt_enable(); > > +} > > +static inline void __rcu_read_lock_bh(void) > > +{ > > + local_bh_disable(); > > + __acquire(RCU_BH); > > + rcu_read_acquire(); > > +} > > +static inline void __rcu_read_unlock_bh(void) > > +{ > > + rcu_read_release(); > > + __release(RCU_BH); > > + local_bh_enable(); > > +} > > + > > +#define __synchronize_sched() synchronize_rcu() > > + > > +#define call_rcu_sched(head, func) call_rcu(head, func) > > + > > +static inline void rcu_init_sched(void) > > +{ > > +} > > + > > +extern void __rcu_init(void); > > +extern void rcu_check_callbacks(int cpu, int user); > > +extern void rcu_restart_cpu(int cpu); > > + > > +extern long rcu_batches_completed(void); > > +extern long rcu_batches_completed_bh(void); > > + > > +#ifdef CONFIG_NO_HZ > > +void rcu_enter_nohz(void); > > +void rcu_exit_nohz(void); > > +#else /* CONFIG_NO_HZ */ > > +static inline void rcu_enter_nohz(void) > > +{ > > +} > > +static inline void rcu_exit_nohz(void) > > +{ > > +} > > +#endif /* CONFIG_NO_HZ */ > > + > > +#endif /* __LINUX_RCUTREE_H */ > > diff --git a/init/Kconfig b/init/Kconfig > > index b678803..6fdca78 100644 > > --- a/init/Kconfig > > +++ b/init/Kconfig > > @@ -914,10 +914,16 @@ source "block/Kconfig" > > config PREEMPT_NOTIFIERS > > bool > > > > -config CLASSIC_RCU > > - def_bool !PREEMPT_RCU > > +config TREE_RCU_TRACE > > + def_bool RCU_TRACE && TREE_RCU > > + select DEBUG_FS > > help > > - This option selects the classic RCU implementation that is > > - designed for best read-side performance on non-realtime > > - systems. Classic RCU is the default. Note that the > > - PREEMPT_RCU symbol is used to select/deselect this option. > > + This option provides tracing for the TREE_RCU implementation, > > + permitting Makefile to trivially select kernel/rcutree_trace.c. > > + > > +config PREEMPT_RCU_TRACE > > + def_bool RCU_TRACE && PREEMPT_RCU > > + select DEBUG_FS > > + help > > + This option provides tracing for the PREEMPT_RCU implementation, > > + permitting Makefile to trivially select kernel/rcupreempt_trace.c. > > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt > > index 9fdba03..463f297 100644 > > --- a/kernel/Kconfig.preempt > > +++ b/kernel/Kconfig.preempt > > @@ -52,10 +52,29 @@ config PREEMPT > > > > endchoice > > > > +choice > > + prompt "RCU Implementation" > > + default CLASSIC_RCU > > + > > +config CLASSIC_RCU > > + bool "Classic RCU" > > + help > > + This option selects the classic RCU implementation that is > > + designed for best read-side performance on non-realtime > > + systems. > > + > > + Select this option if you are unsure. > > + > > +config TREE_RCU > > + bool "Tree-based hierarchical RCU" > > + help > > + This option selects the RCU implementation that is > > + designed for very large SMP system with hundreds or > > + thousands of CPUs. > > + > > config PREEMPT_RCU > > bool "Preemptible RCU" > > depends on PREEMPT > > - default n > > help > > This option reduces the latency of the kernel by making certain > > RCU sections preemptible. Normally RCU code is non-preemptible, if > > @@ -64,16 +83,47 @@ config PREEMPT_RCU > > now-naive assumptions about each RCU read-side critical section > > remaining on a given CPU through its execution. > > > > - Say N if you are unsure. > > +endchoice > > > > config RCU_TRACE > > - bool "Enable tracing for RCU - currently stats in debugfs" > > - depends on PREEMPT_RCU > > - select DEBUG_FS > > - default y > > + bool "Enable tracing for RCU" > > + depends on TREE_RCU || PREEMPT_RCU > > help > > This option provides tracing in RCU which presents stats > > in debugfs for debugging RCU implementation. > > > > Say Y here if you want to enable RCU tracing > > Say N if you are unsure. > > + > > +config RCU_FANOUT > > + int "Tree-based hierarchical RCU fanout value" > > + range 2 64 if 64BIT > > + range 2 32 if !64BIT > > + depends on TREE_RCU > > + default 64 if 64BIT > > + default 32 if !64BIT > > + help > > + This option controls the fanout of hierarchical implementations > > + of RCU, allowing RCU to work efficiently on machines with > > + large numbers of CPUs. This value must be at least the cube > > + root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit > > + systems and up to 262,144 for 64-bit systems. > > + > > + Select a specific number if testing RCU itself. > > + Take the default if unsure. > > + > > +config RCU_FANOUT_EXACT > > + bool "Disable tree-based hierarchical RCU auto-balancing" > > + depends on TREE_RCU > > + default n > > + help > > + This option forces use of the exact RCU_FANOUT value specified, > > + regardless of imbalances in the hierarchy. This is useful for > > + testing RCU itself, and might one day be useful on systems with > > + strong NUMA behavior. > > + > > + Without RCU_FANOUT_EXACT, the code will balance the hierarchy. > > + > > + Say n if unsure. > > + > > + > > diff --git a/kernel/Makefile b/kernel/Makefile > > index 4e1d7df..101e880 100644 > > --- a/kernel/Makefile > > +++ b/kernel/Makefile > > @@ -74,10 +74,10 @@ obj-$(CONFIG_GENERIC_HARDIRQS) += irq/ > > obj-$(CONFIG_SECCOMP) += seccomp.o > > obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o > > obj-$(CONFIG_CLASSIC_RCU) += rcuclassic.o > > +obj-$(CONFIG_TREE_RCU) += rcutree.o > > obj-$(CONFIG_PREEMPT_RCU) += rcupreempt.o > > -ifeq ($(CONFIG_PREEMPT_RCU),y) > > -obj-$(CONFIG_RCU_TRACE) += rcupreempt_trace.o > > -endif > > +obj-$(CONFIG_TREE_RCU_TRACE) += rcutree_trace.o > > +obj-$(CONFIG_PREEMPT_RCU_TRACE) += rcupreempt_trace.o > > obj-$(CONFIG_RELAY) += relay.o > > obj-$(CONFIG_SYSCTL) += utsname_sysctl.o > > obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o > > diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c > > index 2782793..6bc8489 100644 > > --- a/kernel/rcupreempt.c > > +++ b/kernel/rcupreempt.c > > @@ -559,6 +559,16 @@ void rcu_irq_exit(void) > > } > > } > > > > +void rcu_nmi_enter(void) > > +{ > > + rcu_irq_enter(); > > +} > > + > > +void rcu_nmi_exit(void) > > +{ > > + rcu_irq_exit(); > > +} > > + > > static void dyntick_save_progress_counter(int cpu) > > { > > struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); > > diff --git a/kernel/rcupreempt_trace.c b/kernel/rcupreempt_trace.c > > index 5edf82c..def42e8 100644 > > --- a/kernel/rcupreempt_trace.c > > +++ b/kernel/rcupreempt_trace.c > > @@ -149,12 +149,12 @@ static void rcupreempt_trace_sum(struct rcupreempt_trace *sp) > > sp->done_length += cp->done_length; > > sp->done_add += cp->done_add; > > sp->done_remove += cp->done_remove; > > - atomic_set(&sp->done_invoked, atomic_read(&cp->done_invoked)); > > + atomic_add(atomic_read(&cp->done_invoked), &sp->done_invoked); > > sp->rcu_check_callbacks += cp->rcu_check_callbacks; > > - atomic_set(&sp->rcu_try_flip_1, > > - atomic_read(&cp->rcu_try_flip_1)); > > - atomic_set(&sp->rcu_try_flip_e1, > > - atomic_read(&cp->rcu_try_flip_e1)); > > + atomic_add(atomic_read(&cp->rcu_try_flip_1), > > + &sp->rcu_try_flip_1); > > + atomic_add(atomic_read(&cp->rcu_try_flip_e1), > > + &sp->rcu_try_flip_e1); > > sp->rcu_try_flip_i1 += cp->rcu_try_flip_i1; > > sp->rcu_try_flip_ie1 += cp->rcu_try_flip_ie1; > > sp->rcu_try_flip_g1 += cp->rcu_try_flip_g1; > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > new file mode 100644 > > index 0000000..d0852c8 > > --- /dev/null > > +++ b/kernel/rcutree.c > > @@ -0,0 +1,1510 @@ > > +/* > > + * Read-Copy Update mechanism for mutual exclusion > > + * > > + * This program is free software; you can redistribute it and/or modify > > + * it under the terms of the GNU General Public License as published by > > + * the Free Software Foundation; either version 2 of the License, or > > + * (at your option) any later version. > > + * > > + * This program is distributed in the hope that it will be useful, > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > + * GNU General Public License for more details. > > + * > > + * You should have received a copy of the GNU General Public License > > + * along with this program; if not, write to the Free Software > > + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. > > + * > > + * Copyright IBM Corporation, 2008 > > + * > > + * Authors: Dipankar Sarma > > + * Manfred Spraul > > + * Paul E. McKenney Hierarchical version > > + * > > + * Based on the original work by Paul McKenney > > + * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. > > + * > > + * For detailed explanation of Read-Copy Update mechanism see - > > + * Documentation/RCU > > + */ > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC > > +static struct lock_class_key rcu_lock_key; > > +struct lockdep_map rcu_lock_map = > > + STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); > > +EXPORT_SYMBOL_GPL(rcu_lock_map); > > +#endif > > + > > +/* Data structures. */ > > + > > +#define RCU_STATE_INITIALIZER(name) { \ > > + .level = { &name.node[0] }, \ > > + .levelcnt = { \ > > + NUM_RCU_LVL_0, /* root of hierarchy. */ \ > > + NUM_RCU_LVL_1, \ > > + NUM_RCU_LVL_2, \ > > + NUM_RCU_LVL_3, /* == MAX_RCU_LVLS */ \ > > + }, \ > > + .signaled = RCU_SIGNAL_INIT, \ > > + .gpnum = -300, \ > > + .completed = -300, \ > > + .onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \ > > + .fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \ > > + .n_force_qs = 0, \ > > + .n_force_qs_ngp = 0, \ > > +} > > + > > +struct rcu_state rcu_state = RCU_STATE_INITIALIZER(rcu_state); > > +DEFINE_PER_CPU(struct rcu_data, rcu_data); > > + > > +struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state); > > +DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); > > + > > +#ifdef CONFIG_NO_HZ > > +DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks); > > +#endif /* #ifdef CONFIG_NO_HZ */ > > + > > +static int blimit = 10; /* Maximum callbacks per softirq. */ > > +static int qhimark = 10000; /* If this many pending, ignore blimit. */ > > +static int qlowmark = 100; /* Once only this many pending, use blimit. */ > > + > > +static void force_quiescent_state(struct rcu_state *rsp, int relaxed); > > + > > +/* > > + * Return the number of RCU batches processed thus far for debug & stats. > > + */ > > +long rcu_batches_completed(void) > > +{ > > + return rcu_state.completed; > > +} > > +EXPORT_SYMBOL_GPL(rcu_batches_completed); > > + > > +/* > > + * Return the number of RCU BH batches processed thus far for debug & stats. > > + */ > > +long rcu_batches_completed_bh(void) > > +{ > > + return rcu_bh_state.completed; > > +} > > +EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); > > + > > +/* > > + * Does the CPU have callbacks ready to be invoked? > > + */ > > +static int > > +cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) > > +{ > > + return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]; > > +} > > + > > +/* > > + * Does the current CPU require a yet-as-unscheduled grace period? > > + */ > > +static int > > +cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + /* ACCESS_ONCE() because we are accessing outside of lock. */ > > + return *rdp->nxttail[RCU_DONE_TAIL] && > > + ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum); > > +} > > + > > +/* > > + * Return the root node of the specified rcu_state structure. > > + */ > > +static struct rcu_node *rcu_get_root(struct rcu_state *rsp) > > +{ > > + return &rsp->node[0]; > > +} > > + > > +#ifdef CONFIG_SMP > > + > > +/* > > + * If the specified CPU is offline, tell the caller that it is in > > + * a quiescent state. Otherwise, whack it with a reschedule IPI. > > + * Grace periods can end up waiting on an offline CPU when that > > + * CPU is in the process of coming online -- it will be added to the > > + * rcu_node bitmasks before it actually makes it online. > => > This can also happen when a CPU has just gone offline, > but RCU hasn't yet marked it as offline. However, it's impact > on delaying the grace period may not be high as in the > CPU-online case. Good point -- I updated the comment to include the going-offline case. > > + * Because this > > + * race is quite rare, we check for it after detecting that the grace > > + * period has been delayed rather than checking each and every CPU > > + * each and every time we start a new grace period. > > + */ > > +static int rcu_implicit_offline_qs(struct rcu_data *rdp) > > +{ > > + /* > > + * If the CPU is offline, it is in a quiescent state. We can > > + * trust its state not to change because interrupts are disabled. > > + */ > > + if (cpu_is_offline(rdp->cpu)) { > > + rdp->offline_fqs++; > > + return 1; > > + } > > + > > + /* The CPU is online, so send it a reschedule IPI. */ > > + if (rdp->cpu != smp_processor_id()) > => > This check is safe here since this callpath is invoked > from a softirq, and thus the system cannot do a stop_machine() > as yet. This implies that the cpu in question cannot go offline > until we're done. Yep! I note that in the comment preceding the cpu_is_offline() above. Is that sufficient, or should I reiterate that point in another comment here? > > + smp_send_reschedule(rdp->cpu); > > + else > > + set_need_resched(); > > + rdp->resched_ipi++; > > + return 0; > > +} > > + > > +#endif /* #ifdef CONFIG_SMP */ > > + > > +#ifdef CONFIG_NO_HZ > > +static DEFINE_RATELIMIT_STATE(rcu_rs, 10 * HZ, 5); > > + > > +/* > > + * Enter nohz mode, in other words, -leave- the mode in which RCU > > + * read-side critical sections can occur. (Though RCU read-side > > + * critical sections can occur in irq handlers in nohz mode, a possibility > > + * handled by rcu_irq_enter() and rcu_irq_exit()). > > + */ > > +void rcu_enter_nohz(void) > > +{ > > + unsigned long flags; > > + struct rcu_dynticks *rdtp; > > + > > + smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */ > > + local_irq_save(flags); > > + rdtp = &__get_cpu_var(rcu_dynticks); > > + rdtp->dynticks++; > > + rdtp->dynticks_nesting++; > > + WARN_ON_RATELIMIT(__get_cpu_var(rcu_dynticks).dynticks & 0x1, &rcu_rs); > > + local_irq_restore(flags); > > +} > > + > > +/* > > + * Exit nohz mode. > > + */ > > +void rcu_exit_nohz(void) > > +{ > > + unsigned long flags; > > + struct rcu_dynticks *rdtp; > > + > > + local_irq_save(flags); > > + rdtp = &__get_cpu_var(rcu_dynticks); > > + rdtp->dynticks++; > > + rdtp->dynticks_nesting--; > > + WARN_ON_RATELIMIT(!(__get_cpu_var(rcu_dynticks).dynticks & 0x1), > > + &rcu_rs); > > + local_irq_restore(flags); > > + smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */ > > +} > > + > > +/** > > + * rcu_nmi_enter - Called from NMI > > + * > > + * If the CPU was idle with dynamic ticks active, and there is no > > + * irq handler running, this updates rdtp->dynticks_nmi to let the > > + * RCU grace-period handling know that the CPU is active. > > + */ > > +void rcu_nmi_enter(void) > > +{ > > + struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); > > + > > + if (rdtp->dynticks & 0x1) > > + return; > > + rdtp->dynticks_nmi++; > > + WARN_ON_RATELIMIT(!(rdtp->dynticks_nmi & 0x1), &rcu_rs); > > +} > > + > > +/** > > + * rcu_nmi_exit - Called from NMI > > + * > > + * If the CPU was idle with dynamic ticks active, and there is no > > + * irq handler running, this updates rdtp->dynticks_nmi to let the > > + * RCU grace-period handling know that the CPU is no longer active. > > + */ > > +void rcu_nmi_exit(void) > > +{ > > + struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); > > + > > + if (rdtp->dynticks & 0x1) > > + return; > > + rdtp->dynticks_nmi++; > > + WARN_ON_RATELIMIT(rdtp->dynticks_nmi & 0x1, &rcu_rs); > > +} > > + > > +/** > > + * rcu_irq_enter - Called from hard irq handlers > > + * > > + * If the CPU was idle with dynamic ticks active, this updates the > > + * rdtp->dynticks to let the RCU handling know that the CPU is active. > > + */ > > +void rcu_irq_enter(void) > > +{ > > + struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); > > + > > + if (rdtp->dynticks_nesting++) > > + return; > > + rdtp->dynticks++; > > + WARN_ON_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs); > > +} > > + > > +/** > > + * rcu_irq_exit - Called when exiting hard irq context. > > + * > > + * If the CPU was idle with dynamic ticks active, update the rdp->dynticks > > + * to put let the RCU handling be aware that the CPU is going back to idle > > + * with no ticks. > > + */ > > +void rcu_irq_exit(void) > > +{ > > + struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); > > + > > + if (--rdtp->dynticks_nesting) > > + return; > > + rdtp->dynticks++; > > + WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs); > > + > > + /* If the interrupt queued a callback, get out of dyntick mode. */ > > + if (__get_cpu_var(rcu_data).nxtlist || > > + __get_cpu_var(rcu_bh_data).nxtlist) > > + set_need_resched(); > > => Just wondering, can't NMI handlers queue callbacks? If yes, > isn't this check needed in rcu_nmi_exit() as well ? NMI handlers are forbidden to queue callbacks, as the current call_rcu() implementation is not NMI-safe. It would be possible to create an NMI-safe implementation, but there needs to be someone who needs it -really- badly to justify the added complexity. ;-) > > +} > > + > > +/* > > + * Record the specified "completed" value, which is later used to validate > > + * dynticks counter manipulations. Specify "rsp->complete - 1" to > => ^^^^^^^^^^^^^^^^^^^ > "rsp->completed - 1" ? Good catch! Fixed. > > + * unconditionally invalidate any future dynticks manipulations (which is > > + * useful at the beginning of a grace period). > > + */ > > +static void dyntick_record_completed(struct rcu_state *rsp, int comp) > > +{ > > + rsp->dynticks_completed = comp; > > +} > > + > > +#ifdef CONFIG_SMP > > + > > +/* > > + * Recall the previously recorded value of the completion for dynticks. > > + */ > > +static long dyntick_recall_completed(struct rcu_state *rsp) > > +{ > > + return rsp->dynticks_completed; > > +} > > + > > +/* > > + * Snapshot the specified CPU's dynticks counter so that we can later > > + * credit them with an implicit quiescent state. Return 1 if this CPU > > + * is already in a quiescent state courtesy of dynticks idle mode. > > + */ > > +static int dyntick_save_progress_counter(struct rcu_data *rdp) > > +{ > > + int ret; > > + int snap; > > + int snap_nmi; > > + > > + snap = rdp->dynticks->dynticks; > > + snap_nmi = rdp->dynticks->dynticks_nmi; > > + smp_mb(); /* Order sampling of snap with end of grace period. */ > > + rdp->dynticks_snap = snap; > > + rdp->dynticks_nmi_snap = snap_nmi; > > + ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0); > > + if (ret) > > + rdp->dynticks_fqs++; > > + return ret; > > +} > > + > > +/* > > + * Return true if the specified CPU has passed through a quiescent > > + * state by virtue of being in or having passed through an dynticks > > + * idle state since the last call to dyntick_save_progress_counter() > > + * for this same CPU. > > + */ > > +static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) > > +{ > > + long curr; > > + long curr_nmi; > > + long snap; > > + long snap_nmi; > > + > > + curr = rdp->dynticks->dynticks; > > + snap = rdp->dynticks_snap; > > + curr_nmi = rdp->dynticks->dynticks_nmi; > > + snap_nmi = rdp->dynticks_nmi_snap; > > + smp_mb(); /* force ordering with cpu entering/leaving dynticks. */ > > + > > + /* > > + * If the CPU passed through or entered a dynticks idle phase with > > + * no active irq/NMI handlers, then we can safely pretend that the CPU > > + * already acknowledged the request to pass through a quiescent > > + * state. Either way, that CPU cannot possibly be in an RCU > > + * read-side critical section that started before the beginning > > + * of the current RCU grace period. > > + */ > > + if ((curr != snap || (curr & 0x1) == 0) && > > + (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) { > > + rdp->dynticks_fqs++; > > + return 1; > > + } > > + > > + /* Go check for the CPU being offline. */ > > + return rcu_implicit_offline_qs(rdp); > > +} > > + > > +#endif /* #ifdef CONFIG_SMP */ > > + > > +#else /* #ifdef CONFIG_NO_HZ */ > > + > > +static void dyntick_record_completed(struct rcu_state *rsp, int comp) > > +{ > > +} > > + > > +#ifdef CONFIG_SMP > > + > > +/* > > + * If there are no dynticks, then the only way that a CPU can passively > > + * be in a quiescent state is to be offline. Unlike dynticks idle, which > > + * is a point in time during the prior (already finished) grace period, > > + * an offline CPU is always in a quiescent state, and thus can be > > + * unconditionally applied. So just return the current value of completed. > > + */ > > +static long dyntick_recall_completed(struct rcu_state *rsp) > > +{ > > + return rsp->completed; > > +} > > + > > +static int dyntick_save_progress_counter(struct rcu_data *rdp) > > +{ > > + return 0; > > +} > > + > > +static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) > > +{ > > + return rcu_implicit_offline_qs(rdp); > > +} > > + > > +#endif /* #ifdef CONFIG_SMP */ > > + > > +#endif /* #else #ifdef CONFIG_NO_HZ */ > > + > > +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR > > + > > +static void record_gp_stall_check_time(struct rcu_state *rsp) > > +{ > > + rsp->gp_start = jiffies; > > + rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK; > > +} > > + > > +static void print_other_cpu_stall(struct rcu_state *rsp) > > +{ > > + int cpu; > > + long delta; > > + unsigned long flags; > > + struct rcu_node *rnp = rcu_get_root(rsp); > > + struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1]; > > + struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES]; > > + > > + /* Only let one CPU complain about others per time interval. */ > > + > > + spin_lock_irqsave(&rnp->lock, flags); > > + delta = jiffies - rsp->jiffies_stall; > > + if (delta < RCU_STALL_RAT_DELAY || rsp->gpnum != rsp->completed) { > => ----------------> [1] > See comment in check_cpu_stall() > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + return; > > + } > > + rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + > > + /* OK, time to rat on our buddy... */ > > + > > + printk(KERN_ERR "RCU detected CPU stalls:"); > > + for (; rnp_cur < rnp_end; rnp_cur++) { > > + if (rnp_cur->qsmask == 0) > > + continue; > > + for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++) > > + if (rnp_cur->qsmask & (1UL << cpu)) > > + printk(" %d", rnp_cur->grplo + cpu); > > + } > > + printk(" (detected by %d, t=%ld jiffies)\n", > > + smp_processor_id(), (long)(jiffies - rsp->gp_start)); > > + force_quiescent_state(rsp, 0); /* Kick them all. */ > > +} > > + > > +static void print_cpu_stall(struct rcu_state *rsp) > > +{ > > + unsigned long flags; > > + struct rcu_node *rnp = rcu_get_root(rsp); > > + > > + printk(KERN_ERR "RCU detected CPU %d stall (t=%lu jiffies)\n", > > + smp_processor_id(), jiffies - rsp->gp_start); > > + dump_stack(); > > + spin_lock_irqsave(&rnp->lock, flags); > > + if ((long)(jiffies - rsp->jiffies_stall) >= 0) > > + rsp->jiffies_stall = > > + jiffies + RCU_SECONDS_TILL_STALL_RECHECK; > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + set_need_resched(); /* kick ourselves to get things going. */ > > +} > > + > > +static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + long delta; > > + struct rcu_node *rnp; > > + > > + delta = jiffies - rsp->jiffies_stall; > > + rnp = rdp->mynode; > > + if ((rnp->qsmask & rdp->grpmask) && delta >= 0) { > > + > > + /* We haven't checked in, so go dump stack. */ > > + print_cpu_stall(rsp); > > + > > + } else if (rsp->gpnum != rsp->completed && > > + delta >= RCU_STALL_RAT_DELAY) { > > => If this condition is true, then, > rsp->gpnum != rsp->completed. Hence, we will always enter > the if() condition in print_other_cpu_stall() at > [1] (See above), and return without ratting our buddy. > > That defeats the purpose of the stall check or I am > missing the obvious, which is quite possible :-) Let's see... The goal of this code is as follows: o If possible, we want the stalled CPU to dump its own stack, since self-stack-tracing is more reliable. (In fact, the code simply declines to do stack traces on other CPUs.) o But if the stalled CPU doesn't dump its own stack, we do want some other CPU to at least call attention to the stalled CPU. o If 4095 CPUs all note that a given CPU is stalled, we really don't want 4096 concurrent intermixed complaints on the console. So the idea is that print_other_cpu_stall() acquires rnp->lock, and rechecks the jiffies ("<" in print_other_cpu_stall() vs. ">=" in check_cpu_stall()). Only the first guy in will complain. Make sense, or did I mess up something? > > + > > + /* They had two time units to dump stack, so complain. */ > > + print_other_cpu_stall(rsp); > > + } > > +} > > + > > +#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ > > + > > +static void record_gp_stall_check_time(struct rcu_state *rsp) > > +{ > > +} > > + > > +static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > +} > > + > > +#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ > > + > > +/* > > + * Update CPU-local rcu_data state to record the newly noticed grace period. > > + * This is used both when we started the grace period and when we notice > > + * that someone else started the grace period. > > + */ > > +static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + rdp->qs_pending = 1; > > + rdp->passed_quiesc = 0; > > + rdp->gpnum = rsp->gpnum; > > +} > > + > > +/* > > + * Did someone else start a new RCU grace period start since we last > > + * checked? Update local state appropriately if so. Must be called > > + * on the CPU corresponding to rdp. > > + */ > > +static int > > +check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + unsigned long flags; > > + int ret = 0; > > + > > + local_irq_save(flags); > > + if (rdp->gpnum != rsp->gpnum) { > > + note_new_gpnum(rsp, rdp); > > + ret = 1; > > + } > > + local_irq_restore(flags); > > + return ret; > > +} > > + > > +/* > > + * Start a new RCU grace period if warranted, re-initializing the hierarchy > > + * in preparation for detecting the next grace period. The caller must hold > > + * the root node's ->lock, which is released before return. Hard irqs must > > + * be disabled. > > + */ > > +static void > > +rcu_start_gp(struct rcu_state *rsp, unsigned long iflg) > > + __releases(rsp->rda[smp_processor_id()]->lock) > > +{ > > + unsigned long flags = iflg; > > + struct rcu_data *rdp = rsp->rda[smp_processor_id()]; > > + struct rcu_node *rnp = rcu_get_root(rsp); > > + struct rcu_node *rnp_cur; > > + struct rcu_node *rnp_end; > > + > > + if (!cpu_needs_another_gp(rsp, rdp)) { > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + return; > > + } > > + > > + /* Advance to a new grace period and initialize state. */ > > + rsp->gpnum++; > > + rsp->signaled = RCU_SIGNAL_INIT; > > + rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; > > + record_gp_stall_check_time(rsp); > > + dyntick_record_completed(rsp, rsp->completed - 1); > > + note_new_gpnum(rsp, rdp); > > + > > + /* > > + * Because we are first, we know that all our callbacks will > > + * be covered by this upcoming grace period, even the ones > > + * that were registered arbitrarily recently. > > + */ > > + rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; > > + rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; > > + > > + /* Special-case the common single-level case. */ > > + if (NUM_RCU_NODES == 1) { > > + rnp->qsmask = rnp->qsmaskinit; > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + return; > > + } > > + > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + > > + > > + /* Exclude any concurrent CPU-hotplug operations. */ > > + spin_lock_irqsave(&rsp->onofflock, flags); > > + > > + /* > > + * Set the quiescent-state-needed bits in all the non-leaf RCU > > + * nodes for all currently online CPUs. This operation relies > > + * on the layout of the hierarchy within the rsp->node[] array. > > + * Note that other CPUs will access only the leaves of the > > + * hierarchy, which still indicate that no grace period is in > > + * progress. In addition, we have excluded CPU-hotplug operations. > > + * > > + * We therefore do not need to hold any locks. Any required > > + * memory barriers will be supplied by the locks guarding the > > + * leaf rcu_nodes in the hierarchy. > > + */ > > + > > + rnp_end = rsp->level[NUM_RCU_LVLS - 1]; > > + for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) > > + rnp_cur->qsmask = rnp_cur->qsmaskinit; > > + > > + /* > > + * Now set up the leaf nodes. Here we must be careful. First, > > + * we need to hold the lock in order to exclude other CPUs, which > > + * might be contending for the leaf nodes' locks. Second, as > > + * soon as we initialize a given leaf node, its CPUs might run > > + * up the rest of the hierarchy. We must therefore acquire locks > > + * for each node that we touch during this stage. (But we still > > + * are excluding CPU-hotplug operations.) > > + * > > + * Note that the grace period cannot complete until we finish > > + * the initialization process, as there will be at least one > > + * qsmask bit set in the root node until that time, namely the > > + * one corresponding to this CPU. > > + */ > > + rnp_end = &rsp->node[NUM_RCU_NODES]; > > + rnp_cur = rsp->level[NUM_RCU_LVLS - 1]; > > + for (; rnp_cur < rnp_end; rnp_cur++) { > > + spin_lock(&rnp_cur->lock); /* irqs already disabled. */ > > + rnp_cur->qsmask = rnp_cur->qsmaskinit; > > + spin_unlock(&rnp_cur->lock); /* irqs already disabled. */ > > + } > > + > > + spin_unlock_irqrestore(&rsp->onofflock, flags); > > +} > > + > > +/* > > + * Advance this CPU's callbacks, but only if the current grace period > > + * has ended. This may be called only from the CPU to whom the rdp > > + * belongs. > > + */ > > +static void > > +rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + long completed_snap; > > + unsigned long flags; > > + > > + local_irq_save(flags); > > + completed_snap = ACCESS_ONCE(rsp->completed); /* outside of lock. */ > > + > > + /* Did another grace period end? */ > > + if (rdp->completed != completed_snap) { > > + > > + /* Advance callbacks. No harm if list empty. */ > > + rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL]; > > + rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL]; > > + rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; > > + > > + /* Remember that we saw this grace-period completion. */ > > + rdp->completed = completed_snap; > > + } > > + local_irq_restore(flags); > > +} > > + > > +/* > > + * Similar to cpu_quiet(), for which it is a helper function. Allows > > + * a group of CPUs to be quieted at one go, though all the CPUs in the > > + * group must be represented by the same leaf rcu_node structure. > > + * That structure's lock must be held upon entry, and it is released > > + * before return. > > + */ > > +static void > > +cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp, > > + unsigned long flags) > > + __releases(rnp->lock) > > +{ > > + /* Walk up the rcu_node hierarchy. */ > > + for (;;) { > > + if (!(rnp->qsmask & mask)) { > > + > > + /* Our bit has already been cleared, so done. */ > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + return; > > + } > > + rnp->qsmask &= ~mask; > > + if (rnp->qsmask != 0) { > > + > > + /* Other bits still set at this level, so done. */ > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + return; > > + } > > + mask = rnp->grpmask; > > + if (rnp->parent == NULL) { > > + > > + /* No more levels. Exit loop holding root lock. */ > > + > > + break; > > + } > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + rnp = rnp->parent; > > + spin_lock_irqsave(&rnp->lock, flags); > > + } > > + > > + /* > > + * Get here if we are the last CPU to pass through a quiescent > > + * state for this grace period. Clean up and let rcu_start_gp() > > + * start up the next grace period if one is needed. Note that > > + * we still hold rnp->lock, as required by rcu_start_gp(), which > > + * will release it. > > + */ > > + rsp->completed = rsp->gpnum; > > + rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]); > > + rcu_start_gp(rsp, flags); /* releases rnp->lock. */ > > +} > > + > > +/* > > + * Record a quiescent state for the specified CPU, which must either be > > + * the current CPU or an offline CPU. When invoking this on one's own > > + * behalf, lastcomp is used to make sure we are still in the grace period > > + * of interest. We don't want to end the current grace period based on > > + * quiescent states detected in an earlier grace period! On the other hand, > > + * it the CPU being quieted is offline, we can safely pass in lastcomp==NULL, > > + * since an offline CPU is in a quiescent state with respect to any grace > > + * period, unlike pesky online CPUs, which can go non-quiescent with > > + * absolutely no warning. > > + */ > > +static void > > +cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long *lastcomp) > > +{ > > + unsigned long flags; > > + unsigned long mask; > > + struct rcu_node *rnp; > > + > > + rnp = rdp->mynode; > > + spin_lock_irqsave(&rnp->lock, flags); > > + if (lastcomp != NULL && > > + *lastcomp != ACCESS_ONCE(rsp->completed)) { > > + > > + /* > > + * Someone beat us to it for this grace period, so leave. > > + * The race with GP start is resolved by the fact that we > > + * hold the leaf rcu_node lock, so that the per-CPU bits > > + * cannot yet be initialized -- so we would simply find our > > + * CPU's bit already cleared in cpu_quiet_msk() if this race > > + * occurred. > > + */ > > + rdp->passed_quiesc = 0; /* try again later! */ > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + return; > > + } > > + mask = rdp->grpmask; > > + if ((rnp->qsmask & mask) == 0) { > > + spin_unlock_irqrestore(&rnp->lock, flags); > > + } else { > > + rdp->qs_pending = 0; > > + > > + /* > > + * This GP can't end until cpu checks in, so all of our > > + * callbacks can be processed during the next GP. > > + */ > > + rdp = rsp->rda[smp_processor_id()]; > > + rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; > > + > > + cpu_quiet_msk(mask, rsp, rnp, flags); /* releases rnp->lock */ > > + } > > +} > > + > > +/* > > + * Check to see if there is a new grace period of which this CPU > > + * is not yet aware, and if so, set up local rcu_data state for it. > > + * Otherwise, see if this CPU has just passed through its first > > + * quiescent state for this grace period, and record that fact if so. > > + */ > > +static void > > +rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + /* If there is now a new grace period, record and return. */ > > + if (check_for_new_grace_period(rsp, rdp)) > > + return; > > + > > + /* > > + * Does this CPU still need to do its part for current grace period? > > + * If no, return and let the other CPUs do their part as well. > > + */ > > + if (!rdp->qs_pending) > > + return; > > + > > + /* > > + * Was there a quiescent state since the beginning of the grace > > + * period? If no, then exit and wait for the next call. > > + */ > > + if (!rdp->passed_quiesc) > > + return; > > + > > + /* Tell RCU we are done (but cpu_quiet() will be the judge of that). */ > > + cpu_quiet(rdp->cpu, rsp, rdp, &rdp->passed_quiesc_completed); > > +} > > + > > +#ifdef CONFIG_HOTPLUG_CPU > > + > > +/* > > + * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy > > + * and move all callbacks from the outgoing CPU to the current one. > > + */ > > +static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) > > +{ > > + int i; > > + unsigned long flags; > > + unsigned long mask; > > + struct rcu_data *rdp = rsp->rda[cpu]; > > + struct rcu_data *rdp_me; > > + struct rcu_node *rnp; > > + > > + /* Exclude any attempts to start a new grace period. */ > > + spin_lock_irqsave(&rsp->onofflock, flags); > > + > > + /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */ > > + rnp = rdp->mynode; > > + mask = rdp->grpmask; /* rnp->grplo is constant. */ > > + do { > > + spin_lock(&rnp->lock); /* irqs already disabled. */ > > + rnp->qsmaskinit &= ~mask; > > + if (rnp->qsmaskinit != 0) { > > + spin_unlock(&rnp->lock); /* irqs already disabled. */ > > + break; > > + } > > + mask = rnp->grpmask; > > + spin_unlock(&rnp->lock); /* irqs already disabled. */ > > + rnp = rnp->parent; > > + } while (rnp != NULL); > > + > > + spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ > > + > > + /* Being offline is a quiescent state, so go record it. */ > > + cpu_quiet(cpu, rsp, rdp, NULL); > > + > > + /* > > + * Move callbacks from the outgoing CPU to the running CPU. > > + * Note that the outgoing CPU is now quiscent, so it is now > > + * (uncharacteristically) safe to access it rcu_data structure. > > + * Note also that we must carefully retain the order of the > > + * outgoing CPU's callbacks in order for rcu_barrier() to work > > + * correctly. Finally, note that we start all the callbacks > > + * afresh, even those that have passed through a grace period > > + * and are therefore ready to invoke. The theory is that hotplug > > + * events are rare, and that if they are frequent enough to > > + * indefinitely delay callbacks, you have far worse things to > > + * be worrying about. > > + */ > > + rdp_me = rsp->rda[smp_processor_id()]; > > + if (rdp->nxtlist != NULL) { > > + *rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist; > > + rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; > > + rdp->nxtlist = NULL; > > + for (i = 0; i < RCU_NEXT_SIZE; i++) > > + rdp->nxttail[i] = &rdp->nxtlist; > > + rdp_me->qlen += rdp->qlen; > > + rdp->qlen = 0; > > + } > > + local_irq_restore(flags); > > +} > > + > > +/* > > + * Remove the specified CPU from the RCU hierarchy and move any pending > > + * callbacks that it might have to the current CPU. This code assumes > > + * that at least one CPU in the system will remain running at all times. > > + * Any attempt to offline -all- CPUs is likely to strand RCU callbacks. > > + */ > > +static void rcu_offline_cpu(int cpu) > > +{ > > + __rcu_offline_cpu(cpu, &rcu_state); > > + __rcu_offline_cpu(cpu, &rcu_bh_state); > > +} > > + > > +#else /* #ifdef CONFIG_HOTPLUG_CPU */ > > + > > +static void rcu_offline_cpu(int cpu) > > +{ > > +} > > + > > +#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */ > > + > > +/* > > + * Invoke any RCU callbacks that have made it to the end of their grace > > + * period. Thottle as specified by rdp->blimit. > > + */ > > +static void rcu_do_batch(struct rcu_data *rdp) > > +{ > > + unsigned long flags; > > + struct rcu_head *next, *list, **tail; > > + int count; > > + > > + /* If no callbacks are ready, just return.*/ > > + if (!cpu_has_callbacks_ready_to_invoke(rdp)) > > + return; > > + > > + /* > > + * Extract the list of ready callbacks, disabling to prevent > > + * races with call_rcu() from interrupt handlers. > > + */ > > + local_irq_save(flags); > > + list = rdp->nxtlist; > > + rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL]; > > + *rdp->nxttail[RCU_DONE_TAIL] = NULL; > > + tail = rdp->nxttail[RCU_DONE_TAIL]; > > + for (count = RCU_NEXT_SIZE - 1; count >= 0; count--) > > + if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL]) > > + rdp->nxttail[count] = &rdp->nxtlist; > > + local_irq_restore(flags); > > + > > + /* Invoke callbacks. */ > > + count = 0; > > + while (list) { > > + next = list->next; > > + prefetch(next); > > + list->func(list); > > + list = next; > > + if (++count >= rdp->blimit) > > + break; > > + } > > + > > + /* Update count, and requeue any remaining callbacks. */ > > + local_irq_save(flags); > > + rdp->qlen -= count; > > + if (list != NULL) { > > + *tail = rdp->nxtlist; > > + rdp->nxtlist = list; > > + for (count = 0; count < RCU_NEXT_SIZE; count++) > > + if (&rdp->nxtlist == rdp->nxttail[count]) > > + rdp->nxttail[count] = tail; > > + else > > + break; > > + } > > + local_irq_restore(flags); > > + > > + /* Reinstate batch limit if we have worked down the excess. */ > > + if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark) > > + rdp->blimit = blimit; > > + > > + /* Re-raise the RCU softirq if there are callbacks remaining. */ > > + if (cpu_has_callbacks_ready_to_invoke(rdp)) > > + raise_softirq(RCU_SOFTIRQ); > > +} > > + > > +/* > > + * Check to see if this CPU is in a non-context-switch quiescent state > > + * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). > > + * Also schedule the RCU softirq handler. > > + * > > + * This function must be called with hardirqs disabled. It is normally > > + * invoked from the scheduling-clock interrupt. If rcu_pending returns > > + * false, there is no point in invoking rcu_check_callbacks(). > > + */ > > +void rcu_check_callbacks(int cpu, int user) > > +{ > > + if (user || > > + (idle_cpu(cpu) && !in_softirq() && > > + hardirq_count() <= (1 << HARDIRQ_SHIFT))) { > > + > > + /* > > + * Get here if this CPU took its interrupt from user > > + * mode or from the idle loop, and if this is not a > > + * nested interrupt. In this case, the CPU is in > > + * a quiescent state, so count it. > > + * > > + * Also do a memory barrier. This is needed to handle > > + * the case where writes from a preempt-disable section > > + * of code get reordered into schedule() by this CPU's > > + * write buffer. The memory barrier makes sure that > > + * the rcu_qsctr_inc() and rcu_bh_qsctr_inc() are see > > + * by other CPUs to happen after any such write. > > + */ > > + > > + smp_mb(); /* See above block comment. */ > > + rcu_qsctr_inc(cpu); > > + rcu_bh_qsctr_inc(cpu); > > + > > + } else if (!in_softirq()) { > > + > > + /* > > + * Get here if this CPU did not take its interrupt from > > + * softirq, in other words, if it is not interrupting > > + * a rcu_bh read-side critical section. This is an _bh > > + * critical section, so count it. The memory barrier > > + * is needed for the same reason as is the above one. > > + */ > > + > > + smp_mb(); /* See above block comment. */ > > + rcu_bh_qsctr_inc(cpu); > > + } > > + raise_softirq(RCU_SOFTIRQ); > > +} > > + > > +#ifdef CONFIG_SMP > > + > > +/* > > + * Scan the leaf rcu_node structures, processing dyntick state for any that > > + * have not yet encountered a quiescent state, using the function specified. > > + * Returns 1 if the current grace period ends while scanning (possibly > > + * because we made it end). > > + */ > > +static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp, > > + int (*f)(struct rcu_data *)) > > +{ > > + unsigned long bit; > > + int cpu; > > + unsigned long flags; > > + unsigned long mask; > > + struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1]; > > + struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES]; > > + > > + for (; rnp_cur < rnp_end; rnp_cur++) { > > + mask = 0; > > + spin_lock_irqsave(&rnp_cur->lock, flags); > > + if (rsp->completed != lastcomp) { > > + spin_unlock_irqrestore(&rnp_cur->lock, flags); > > + return 1; > > + } > > + if (rnp_cur->qsmask == 0) { > > + spin_unlock_irqrestore(&rnp_cur->lock, flags); > > + continue; > > + } > > + cpu = rnp_cur->grplo; > > + bit = 1; > > + mask = 0; > > + for (; cpu <= rnp_cur->grphi; cpu++, bit <<= 1) { > > + if ((rnp_cur->qsmask & bit) != 0 && f(rsp->rda[cpu])) > > + mask |= bit; > > + } > > + if (mask != 0 && rsp->completed == lastcomp) { > > + > > + /* cpu_quiet_msk() releases rnp_cur->lock. */ > > + cpu_quiet_msk(mask, rsp, rnp_cur, flags); > > + continue; > > + } > > + spin_unlock_irqrestore(&rnp_cur->lock, flags); > > + } > > + return 0; > > +} > > + > > +/* > > + * Force quiescent states on reluctant CPUs, and also detect which > > + * CPUs are in dyntick-idle mode. > > + */ > > +static void force_quiescent_state(struct rcu_state *rsp, int relaxed) > > +{ > > + unsigned long flags; > > + long lastcomp; > > + struct rcu_node *rnp = rcu_get_root(rsp); > > + u8 signaled; > > + > > + if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) > > + return; /* No grace period in progress, nothing to force. */ > > + if (!spin_trylock_irqsave(&rsp->fqslock, flags)) > > + return; /* Someone else is already on the job. */ > > + if (relaxed && (long)(rsp->jiffies_force_qs - jiffies) >= 0) > > + goto unlock_ret; /* no emergency and done recently. */ > > + rsp->n_force_qs++; > > + spin_lock(&rnp->lock); > > + lastcomp = rsp->completed; > > + signaled = rsp->signaled; > > + rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; > > + if (rsp->completed == rsp->gpnum) { > > + rsp->n_force_qs_ngp++; > > + spin_unlock(&rnp->lock); > > + goto unlock_ret; /* no GP in progress, time updated. */ > > + } > > + spin_unlock(&rnp->lock); > > + switch (signaled) { > > + case RCU_SAVE_DYNTICK: > > + > > + if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK) > > + break; /* So gcc recognizes the dead code. */ > > + > > + /* Record dyntick-idle state. */ > > + if (rcu_process_dyntick(rsp, lastcomp, > > + dyntick_save_progress_counter)) > > + goto unlock_ret; > > + > > + /* Update state, record completion counter. */ > > + spin_lock(&rnp->lock); > > + if (lastcomp == rsp->completed) { > > + rsp->signaled = RCU_FORCE_QS; > > + dyntick_record_completed(rsp, lastcomp); > > + } > > + spin_unlock(&rnp->lock); > > + break; > > + > > + case RCU_FORCE_QS: > > + > > + /* Check dyntick-idle state, send IPI to laggarts. */ > > + if (rcu_process_dyntick(rsp, dyntick_recall_completed(rsp), > > + rcu_implicit_dynticks_qs)) > > + goto unlock_ret; > > + > > + /* Leave state in case more forcing is required. */ > > + > > + break; > > + } > > +unlock_ret: > > + spin_unlock_irqrestore(&rsp->fqslock, flags); > > +} > > + > > +#else /* #ifdef CONFIG_SMP */ > > + > > +static void force_quiescent_state(struct rcu_state *rsp, int relaxed) > > +{ > > + set_need_resched(); > > +} > > + > > +#endif /* #else #ifdef CONFIG_SMP */ > > + > > +/* > > + * This does the RCU processing work from softirq context for the > > + * specified rcu_state and rcu_data structures. This may be called > > + * only from the CPU to whom the rdp belongs. > > + */ > > +static void > > +__rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + unsigned long flags; > > + > > + /* > > + * If an RCU GP has gone long enough, go check for dyntick > > + * idle CPUs and, if needed, send resched IPIs. > > + */ > > + if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0) > > + force_quiescent_state(rsp, 1); > > + > > + /* > > + * Advance callbacks in response to end of earlier grace > > + * period that some other CPU ended. > > + */ > > + rcu_process_gp_end(rsp, rdp); > > + > > + /* Update RCU state based on any recent quiescent states. */ > > + rcu_check_quiescent_state(rsp, rdp); > > + > > + /* Does this CPU require a not-yet-started grace period? */ > > + if (cpu_needs_another_gp(rsp, rdp)) { > > + spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags); > > + rcu_start_gp(rsp, flags); /* releases above lock */ > > + } > > + > > + /* If there are callbacks ready, invoke them. */ > > + rcu_do_batch(rdp); > > +} > > + > > +/* > > + * Do softirq processing for the current CPU. > > + */ > > +static void rcu_process_callbacks(struct softirq_action *unused) > > +{ > > + /* > > + * Memory references from any prior RCU read-side critical sections > > + * executed by the interrupted code must be seen before any RCU > > + * grace-period manupulations below. > > + */ > > + smp_mb(); /* See above block comment. */ > > + > > + __rcu_process_callbacks(&rcu_state, &__get_cpu_var(rcu_data)); > > + __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); > > + > > + /* > > + * Memory references from any later RCU read-side critical sections > > + * executed by the interrupted code must be seen after any RCU > > + * grace-period manupulations above. > > + */ > > + smp_mb(); /* See above block comment. */ > > +} > > + > > +static void > > +__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > > + struct rcu_state *rsp) > > +{ > > + unsigned long flags; > > + struct rcu_data *rdp; > > + > > + head->func = func; > > + head->next = NULL; > > + > > + smp_mb(); /* Ensure RCU update seen before callback registry. */ > > + > > + /* > > + * Opportunistically note grace-period endings and beginnings. > > + * Note that we might see a beginning right after we see an > > + * end, but never vice versa, since this CPU has to pass through > > + * a quiescent state betweentimes. > > + */ > > + local_irq_save(flags); > > + rdp = rsp->rda[smp_processor_id()]; > > + rcu_process_gp_end(rsp, rdp); > > + check_for_new_grace_period(rsp, rdp); > > + > > + /* Add the callback to our list. */ > > + *rdp->nxttail[RCU_NEXT_TAIL] = head; > > + rdp->nxttail[RCU_NEXT_TAIL] = &head->next; > > + > > + /* Start a new grace period if one not already started. */ > > + if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) { > > + unsigned long nestflag; > > + struct rcu_node *rnp_root = rcu_get_root(rsp); > > + > > + spin_lock_irqsave(&rnp_root->lock, nestflag); > > + rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */ > > + } > > + > > + /* Force the grace period if too many callbacks or too long waiting. */ > > + if (unlikely(++rdp->qlen > qhimark)) { > > + rdp->blimit = INT_MAX; > > + force_quiescent_state(rsp, 0); > > + } else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0) > > + force_quiescent_state(rsp, 1); > > + local_irq_restore(flags); > > +} > > + > > +/* > > + * Queue an RCU callback for invocation after a grace period. > > + */ > > +void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) > > +{ > > + __call_rcu(head, func, &rcu_state); > > +} > > +EXPORT_SYMBOL_GPL(call_rcu); > > + > > +/* > > + * Queue an RCU for invocation after a quicker grace period. > > + */ > > +void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) > > +{ > > + __call_rcu(head, func, &rcu_bh_state); > > +} > > +EXPORT_SYMBOL_GPL(call_rcu_bh); > > + > > +/* > > + * Check to see if there is any immediate RCU-related work to be done > > + * by the current CPU, for the specified type of RCU, returning 1 if so. > > + * The checks are in order of increasing expense: checks that can be > > + * carried out against CPU-local state are performed first. However, > > + * we must check for CPU stalls first, else we might not get a chance. > > + */ > > +static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) > > +{ > > + /* Check for CPU stalls, if enabled. */ > > + check_cpu_stall(rsp, rdp); > > + > > + /* Is the RCU core waiting for a quiescent state from this CPU? */ > > + if (rdp->qs_pending) > > + return 1; > > + > > + /* Does this CPU have callbacks ready to invoke? */ > > + if (cpu_has_callbacks_ready_to_invoke(rdp)) > > + return 1; > > + > > + /* Has RCU gone idle with this CPU needing another grace period? */ > > + if (cpu_needs_another_gp(rsp, rdp)) > > + return 1; > > + > > + /* Has another RCU grace period completed? */ > > + if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */ > > + return 1; > > + > > + /* Has a new RCU grace period started? */ > > + if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */ > > + return 1; > > + > > + /* Has an RCU GP gone long enough to send resched IPIs &c? */ > > + if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) && > > + (long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0) > > + return 1; > > + > > + /* nothing to do */ > > + return 0; > > +} > > + > > +/* > > + * Check to see if there is any immediate RCU-related work to be done > > + * by the current CPU, returning 1 if so. This function is part of the > > + * RCU implementation; it is -not- an exported member of the RCU API. > > + */ > > +int rcu_pending(int cpu) > > +{ > > + return __rcu_pending(&rcu_state, &per_cpu(rcu_data, cpu)) || > > + __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)); > > +} > > + > > +/* > > + * Check to see if any future RCU-related work will need to be done > > + * by the current CPU, even if none need be done immediately, returning > > + * 1 if so. This function is part of the RCU implementation; it is -not- > > + * an exported member of the RCU API. > > + */ > > +int rcu_needs_cpu(int cpu) > > +{ > > + /* RCU callbacks either ready or pending? */ > > + return per_cpu(rcu_data, cpu).nxtlist || > > + per_cpu(rcu_bh_data, cpu).nxtlist; > > +} > > + > > +/* > > + * Initialize a CPU's per-CPU RCU data. We take this "scorched earth" > > + * approach so that we don't have to worry about how long the CPU has > > + * been gone, or whether it ever was online previously. We do trust the > > + * ->mynode field, as it is constant for a given struct rcu_data and > > + * initialized during early boot. > > + * > > + * Note that only one online or offline event can be happening at a given > > + * time. Note also that we can accept some slop in the rsp->completed > > + * access due to the fact that this CPU cannot possibly have any RCU > > + * callbacks in flight yet. > > + */ > > +static void > > +rcu_init_percpu_data(int cpu, struct rcu_state *rsp) > > +{ > > + unsigned long flags; > > + int i; > > + unsigned long mask; > > + struct rcu_data *rdp = rsp->rda[cpu]; > > + struct rcu_node *rnp = rcu_get_root(rsp); > > + > > + /* Set up local state, ensuring consistent view of global state. */ > > + spin_lock_irqsave(&rnp->lock, flags); > > + rdp->completed = rsp->completed; > > + rdp->gpnum = rsp->completed; > > + rdp->passed_quiesc = 0; /* We could be racing with new GP, */ > > + rdp->qs_pending = 1; /* so set up to respond to current GP. */ > > + rdp->beenonline = 1; /* We have now been online. */ > > + rdp->passed_quiesc_completed = rsp->completed - 1; > > + rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo); > > + rdp->nxtlist = NULL; > > + for (i = 0; i < RCU_NEXT_SIZE; i++) > > + rdp->nxttail[i] = &rdp->nxtlist; > > + rdp->qlen = 0; > > + rdp->blimit = blimit; > > +#ifdef CONFIG_NO_HZ > > + rdp->dynticks = &per_cpu(rcu_dynticks, cpu); > > +#endif /* #ifdef CONFIG_NO_HZ */ > > + rdp->cpu = cpu; > > + spin_unlock(&rnp->lock); /* irqs remain disabled. */ > > + > > + /* > > + * A new grace period might start here. If so, we won't be part > > + * of it, but that is OK, as we are currently in a quiescent state. > > + */ > > + > > + /* Exclude any attempts to start a new GP on large systems. */ > > + spin_lock(&rsp->onofflock); /* irqs already disabled. */ > > + > > + /* Add CPU to rcu_node bitmasks. */ > > + rnp = rdp->mynode; > > + mask = rdp->grpmask; > > + do { > > + /* Exclude any attempts to start a new GP on small systems. */ > > + spin_lock(&rnp->lock); /* irqs already disabled. */ > > + rnp->qsmaskinit |= mask; > > + mask = rnp->grpmask; > > + spin_unlock(&rnp->lock); /* irqs already disabled. */ > > + rnp = rnp->parent; > > + } while (rnp != NULL && !(rnp->qsmaskinit & mask)); > > + > > + spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ > > + > > + /* > > + * A new grace period might start here. If so, we will be part of > > + * it, and its gpnum will be greater than ours, so we will > > + * participate. It is also possible for the gpnum to have been > > + * incremented before this function was called, and the bitmasks > > + * to not be filled out until now, in which case we will also > > + * participate due to our gpnum being behind. > > + */ > > + > > + /* Since it is coming online, the CPU is in a quiescent state. */ > > + cpu_quiet(cpu, rsp, rdp, NULL); > > + local_irq_restore(flags); > > +} > > + > > +static void __cpuinit rcu_online_cpu(int cpu) > > +{ > > +#ifdef CONFIG_NO_HZ > > + struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); > > + > > + rdtp->dynticks_nesting = 1; > > + rdtp->dynticks |= 1; /* need consecutive #s even for hotplug. */ > > + rdtp->dynticks_nmi = (rdtp->dynticks + 1) & ~0x1; > => rdtp->dynticks is odd. Hence rdtp->dynticks + 1 should be even. > Why is the additional & ~0x1 ? Overly extreme paranoia? > > +#endif /* #ifdef CONFIG_NO_HZ */ > > + rcu_init_percpu_data(cpu, &rcu_state); > > + rcu_init_percpu_data(cpu, &rcu_bh_state); > > + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); > > +} > > + > > +/* > > + * Handle CPU online/offline notifcation events. > > + */ > > +static int __cpuinit rcu_cpu_notify(struct notifier_block *self, > > + unsigned long action, void *hcpu) > > +{ > > + long cpu = (long)hcpu; > > + > > + switch (action) { > > + case CPU_UP_PREPARE: > > + case CPU_UP_PREPARE_FROZEN: > > + rcu_online_cpu(cpu); > > + break; > > + case CPU_DEAD: > > + case CPU_DEAD_FROZEN: > > + case CPU_UP_CANCELED: > > + case CPU_UP_CANCELED_FROZEN: > > + rcu_offline_cpu(cpu); > > + break; > > + default: > > + break; > > + } > > + return NOTIFY_OK; > > +} > > + > > +/* > > + * Compute the per-level fanout, either using the exact fanout specified > > + * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT. > > + */ > > +#ifdef CONFIG_RCU_FANOUT_EXACT > > +static void __init rcu_init_levelspread(struct rcu_state *rsp) > > +{ > > + int i; > > + > > + for (i = NUM_RCU_LVLS - 1; i >= 0; i--) > > + rsp->levelspread[i] = CONFIG_RCU_FANOUT; > > +} > > +#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */ > > +static void __init rcu_init_levelspread(struct rcu_state *rsp) > > +{ > > + int ccur; > > + int cprv; > > + int i; > > + > > + cprv = NR_CPUS; > > + for (i = NUM_RCU_LVLS - 1; i >= 0; i--) { > > + ccur = rsp->levelcnt[i]; > > + rsp->levelspread[i] = (cprv + ccur - 1) / ccur; > > + cprv = ccur; > > + } > > +} > > +#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */ > > + > > +/* > > + * Helper function for rcu_init() that initializes one rcu_state structure. > > + */ > > +static void __init rcu_init_one(struct rcu_state *rsp) > > +{ > > + int cpustride = 1; > > + int i; > > + int j; > > + struct rcu_node *rnp; > > + > > + /* Initialize the level-tracking arrays. */ > > + > > + for (i = 1; i < NUM_RCU_LVLS; i++) > > + rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1]; > > + rcu_init_levelspread(rsp); > > + > > + /* Initialize the elements themselves, starting from the leaves. */ > > + > > + for (i = NUM_RCU_LVLS - 1; i >= 0; i--) { > > + cpustride *= rsp->levelspread[i]; > > + rnp = rsp->level[i]; > > + for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) { > > + spin_lock_init(&rnp->lock); > > + rnp->qsmask = 0; > > + rnp->qsmaskinit = 0; > > + rnp->grplo = j * cpustride; > > + rnp->grphi = (j + 1) * cpustride - 1; > > + if (rnp->grphi >= NR_CPUS) > > + rnp->grphi = NR_CPUS - 1; > > + if (i == 0) { > > + rnp->grpnum = 0; > > + rnp->grpmask = 0; > > + rnp->parent = NULL; > > + } else { > > + rnp->grpnum = j % rsp->levelspread[i - 1]; > > + rnp->grpmask = 1UL << rnp->grpnum; > > + rnp->parent = rsp->level[i - 1] + > > + j / rsp->levelspread[i - 1]; > > + } > > + rnp->level = i; > > + } > > + } > > +} > > + > > +/* > > + * Helper macro for __rcu_init(). To be used nowhere else! > > + * Assigns leaf node pointers into each CPU's rcu_data structure. > > + */ > > +#define RCU_DATA_PTR_INIT(rsp, rcu_data) \ > > +do { \ > > + rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \ > > + j = 0; \ > > + for_each_possible_cpu(i) { \ > > + if (i > rnp[j].grphi) \ > > + j++; \ > > + per_cpu(rcu_data, i).mynode = &rnp[j]; \ > > + (rsp)->rda[i] = &per_cpu(rcu_data, i); \ > > + } \ > > +} while (0) > > + > > +static struct notifier_block __cpuinitdata rcu_nb = { > > + .notifier_call = rcu_cpu_notify, > > +}; > > + > > +void __init __rcu_init(void) > > +{ > > + int i; /* All used by RCU_DATA_PTR_INIT(). */ > > + int j; > > + struct rcu_node *rnp; > > + > > + printk(KERN_WARNING "Experimental hierarchical RCU implementation.\n"); > > +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR > > + printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n"); > > +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ > > + rcu_init_one(&rcu_state); > > + RCU_DATA_PTR_INIT(&rcu_state, rcu_data); > > + rcu_init_one(&rcu_bh_state); > > + RCU_DATA_PTR_INIT(&rcu_bh_state, rcu_bh_data); > > + > > + for_each_online_cpu(i) > > + rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)i); > > + /* Register notifier for non-boot CPUs */ > > + register_cpu_notifier(&rcu_nb); > > + printk(KERN_WARNING "Experimental hierarchical RCU init done.\n"); > > +} > > + > > +module_param(blimit, int, 0); > > +module_param(qhimark, int, 0); > > +module_param(qlowmark, int, 0); > > diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c > > new file mode 100644 > > index 0000000..1691327 > > --- /dev/null > > +++ b/kernel/rcutree_trace.c > > @@ -0,0 +1,232 @@ > > +/* > > + * Read-Copy Update tracing for classic implementation > > + * > > + * This program is free software; you can redistribute it and/or modify > > + * it under the terms of the GNU General Public License as published by > > + * the Free Software Foundation; either version 2 of the License, or > > + * (at your option) any later version. > > + * > > + * This program is distributed in the hope that it will be useful, > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > > + * GNU General Public License for more details. > > + * > > + * You should have received a copy of the GNU General Public License > > + * along with this program; if not, write to the Free Software > > + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. > > + * > > + * Copyright IBM Corporation, 2008 > > + * > > + * Papers: http://www.rdrop.com/users/paulmck/RCU > > + * > > + * For detailed explanation of Read-Copy Update mechanism see - > > + * Documentation/RCU > > + * > > + */ > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +static DEFINE_MUTEX(rcuclassic_trace_mutex); > > +static char *rcuclassic_trace_buf; > > +#define RCUPREEMPT_TRACE_BUF_SIZE (512*NR_CPUS) > > + > > +static int print_one_rcu_data(struct rcu_data *rdp, char *buf, char *ebuf) > > +{ > > + int cnt = 0; > > + > > + if (!rdp->beenonline) > > + return 0; > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], > > + "%3d%cc=%ld g=%ld pq=%d pqc=%ld qp=%d", > > + rdp->cpu, > > + cpu_is_offline(rdp->cpu) ? '!' : ' ', > > + rdp->completed, rdp->gpnum, > > + rdp->passed_quiesc, rdp->passed_quiesc_completed, > > + rdp->qs_pending); > > +#ifdef CONFIG_NO_HZ > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], > > + " dt=%d dn=%d df=%lu", > > + rdp->dynticks->dynticks, rdp->dynticks->dynticks_nmi, > > + rdp->dynticks_fqs); > > +#endif /* #ifdef CONFIG_NO_HZ */ > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], > > + " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi); > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], > > + " ql=%ld b=%ld\n", rdp->qlen, rdp->blimit); > > + return cnt; > > +} > > + > > +#define PRINT_RCU_DATA(name, buf, ebuf) \ > > + do { \ > > + int _p_r_d_i; \ > > + \ > > + for_each_possible_cpu(_p_r_d_i) \ > > + (buf) += print_one_rcu_data(&per_cpu(name, _p_r_d_i), \ > > + buf, ebuf); \ > > + } while (0) > > + > > +static ssize_t rcudata_read(struct file *filp, char __user *buffer, > > + size_t count, loff_t *ppos) > > +{ > > + ssize_t bcount; > > + char *buf = rcuclassic_trace_buf; > > + char *ebuf = &rcuclassic_trace_buf[RCUPREEMPT_TRACE_BUF_SIZE]; > > + > > + mutex_lock(&rcuclassic_trace_mutex); > > + buf += snprintf(buf, ebuf - buf, "rcu:\n"); > > + PRINT_RCU_DATA(rcu_data, buf, ebuf); > > + buf += snprintf(buf, ebuf - buf, "rcu_bh:\n"); > > + PRINT_RCU_DATA(rcu_bh_data, buf, ebuf); > > + bcount = simple_read_from_buffer(buffer, count, ppos, > > + rcuclassic_trace_buf, strlen(rcuclassic_trace_buf)); > > + mutex_unlock(&rcuclassic_trace_mutex); > > + return bcount; > > +} > > + > > +static int print_one_rcu_state(struct rcu_state *rsp, char *buf, char *ebuf) > > +{ > > + int cnt = 0; > > + int level = 0; > > + struct rcu_node *rnp; > > + > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], > > + "c=%ld g=%ld s=%d jfq=%ld nfqs=%lu/nfqsng=%lu(%lu)\n", > > + rsp->completed, rsp->gpnum, rsp->signaled, > > + (long)(rsp->jiffies_force_qs - jiffies), > > + rsp->n_force_qs, rsp->n_force_qs_ngp, > > + rsp->n_force_qs - rsp->n_force_qs_ngp); > > + for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < NUM_RCU_NODES; rnp++) { > > + if (rnp->level != level) { > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "\n"); > > + level = rnp->level; > > + } > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], > > + "%lx/%lx %d:%d ^%d ", > > + rnp->qsmask, rnp->qsmaskinit, > > + rnp->grplo, rnp->grphi, rnp->grpnum); > > + } > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "\n"); > > + return cnt; > > +} > > + > > +static ssize_t rcuhier_read(struct file *filp, char __user *buffer, > > + size_t count, loff_t *ppos) > > +{ > > + ssize_t bcount; > > + char *buf = rcuclassic_trace_buf; > > + char *ebuf = &rcuclassic_trace_buf[RCUPREEMPT_TRACE_BUF_SIZE]; > > + > > + mutex_lock(&rcuclassic_trace_mutex); > > + buf += print_one_rcu_state(&rcu_state, buf, ebuf); > > + buf += snprintf(buf, ebuf - buf, "rcu_bh:\n"); > > + buf += print_one_rcu_state(&rcu_bh_state, buf, ebuf); > > + bcount = simple_read_from_buffer(buffer, count, ppos, > > + rcuclassic_trace_buf, strlen(rcuclassic_trace_buf)); > > + mutex_unlock(&rcuclassic_trace_mutex); > > + return bcount; > > +} > > + > > +static ssize_t rcugp_read(struct file *filp, char __user *buffer, > > + size_t count, loff_t *ppos) > > +{ > > + ssize_t bcount; > > + char *buf = rcuclassic_trace_buf; > > + char *ebuf = &rcuclassic_trace_buf[RCUPREEMPT_TRACE_BUF_SIZE]; > > + > > + mutex_lock(&rcuclassic_trace_mutex); > > + buf += snprintf(buf, ebuf - buf, "rcu: completed=%ld gpnum=%ld\n", > > + rcu_state.completed, rcu_state.gpnum); > > + buf += snprintf(buf, ebuf - buf, "rcu_bh: completed=%ld gpnum=%ld\n", > > + rcu_bh_state.completed, rcu_bh_state.gpnum); > > + bcount = simple_read_from_buffer(buffer, count, ppos, > > + rcuclassic_trace_buf, strlen(rcuclassic_trace_buf)); > > + mutex_unlock(&rcuclassic_trace_mutex); > > + return bcount; > > +} > > + > > +static struct file_operations rcudata_fops = { > > + .owner = THIS_MODULE, > > + .read = rcudata_read, > > +}; > > + > > +static struct file_operations rcuhier_fops = { > > + .owner = THIS_MODULE, > > + .read = rcuhier_read, > > +}; > > + > > +static struct file_operations rcugp_fops = { > > + .owner = THIS_MODULE, > > + .read = rcugp_read, > > +}; > > + > > +static struct dentry *rcudir, *datadir, *hierdir, *gpdir; > > +static int rcuclassic_debugfs_init(void) > > +{ > > + rcudir = debugfs_create_dir("rcu", NULL); > > + if (!rcudir) > > + goto out; > > + datadir = debugfs_create_file("rcudata", 0444, rcudir, > > + NULL, &rcudata_fops); > > + if (!datadir) > > + goto free_out; > > + > > + gpdir = debugfs_create_file("rcugp", 0444, rcudir, NULL, &rcugp_fops); > > + if (!gpdir) > > + goto free_out; > > + > > + hierdir = debugfs_create_file("rcuhier", 0444, rcudir, > > + NULL, &rcuhier_fops); > > + if (!hierdir) > > + goto free_out; > > + return 0; > > +free_out: > > + if (datadir) > > + debugfs_remove(datadir); > > + if (gpdir) > > + debugfs_remove(gpdir); > > + debugfs_remove(rcudir); > > +out: > > + return 1; > > +} > > + > > +static int __init rcuclassic_trace_init(void) > > +{ > > + int ret; > > + > > + rcuclassic_trace_buf = kmalloc(RCUPREEMPT_TRACE_BUF_SIZE, GFP_KERNEL); > > + if (!rcuclassic_trace_buf) > > + return 1; > > + ret = rcuclassic_debugfs_init(); > > + if (ret) > > + kfree(rcuclassic_trace_buf); > > + return ret; > > +} > > + > > +static void __exit rcuclassic_trace_cleanup(void) > > +{ > > + debugfs_remove(datadir); > > + debugfs_remove(gpdir); > > + debugfs_remove(hierdir); > > + debugfs_remove(rcudir); > > + kfree(rcuclassic_trace_buf); > > +} > > + > > + > > +module_init(rcuclassic_trace_init); > > +module_exit(rcuclassic_trace_cleanup); > > diff --git a/kernel/softirq.c b/kernel/softirq.c > > index c506f26..ad31780 100644 > > --- a/kernel/softirq.c > > +++ b/kernel/softirq.c > > @@ -256,8 +256,11 @@ void irq_enter(void) > > { > > #ifdef CONFIG_NO_HZ > > int cpu = smp_processor_id(); > > - if (idle_cpu(cpu) && !in_interrupt()) > > - tick_nohz_stop_idle(cpu); > > + if (idle_cpu(cpu)) { > > + if (!in_interrupt()) > > + tick_nohz_stop_idle(cpu); > > + rcu_irq_enter(); > > + } > > #endif > > __irq_enter(); > > #ifdef CONFIG_NO_HZ > > @@ -285,9 +288,11 @@ void irq_exit(void) > > > > #ifdef CONFIG_NO_HZ > > /* Make sure that timer wheel updates are propagated */ > > - if (!in_interrupt() && idle_cpu(smp_processor_id()) && !need_resched()) > > - tick_nohz_stop_sched_tick(0); > > - rcu_irq_exit(); > > + if (idle_cpu(smp_processor_id())) { > > + rcu_irq_exit(); > > + if (!in_interrupt() && !need_resched()) > > + tick_nohz_stop_sched_tick(0); > > + } > > #endif > > preempt_enable_no_resched(); > > } > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 800ac84..804e08c 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -597,6 +597,19 @@ config RCU_TORTURE_TEST_RUNNABLE > > Say N here if you want the RCU torture tests to start only > > after being manually enabled via /proc. > > > > +config RCU_CPU_STALL_DETECTOR > > + bool "Check for stalled CPUs delaying RCU grace periods" > > + depends on CLASSIC_RCU || TREE_RCU > > + default n > > + help > > + This option causes RCU to printk information on which > > + CPUs are delaying the current grace period, but only when > > + the grace period extends for excessive time periods. > > + > > + Say Y if you want RCU to perform such checks. > > + > > + Say N if you are unsure. > > + > > config KPROBES_SANITY_TEST > > bool "Kprobes sanity tests" > > depends on DEBUG_KERNEL > > -- > Thanks and Regards > gautham -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/