Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756050Ab0A0VXW (ORCPT ); Wed, 27 Jan 2010 16:23:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756034Ab0A0VXK (ORCPT ); Wed, 27 Jan 2010 16:23:10 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:50099 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756027Ab0A0VXH (ORCPT ); Wed, 27 Jan 2010 16:23:07 -0500 Date: Wed, 27 Jan 2010 13:22:12 -0800 From: Andrew Morton To: Balbir Singh Cc: mingo@redhat.com, hpa@zytor.com, anton@samba.org, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu, linux-tip-commits@vger.kernel.org Subject: Re: [tip:sched/urgent] sched: cpuacct: Use bigger percpu counter batch values for stats counters Message-Id: <20100127132212.cd43cd94.akpm@linux-foundation.org> In-Reply-To: <661de9471001270534ve6f7bf0nb58ef58f9a6ff10e@mail.gmail.com> References: <20100118044142.GS12666@kryten> <661de9471001270534ve6f7bf0nb58ef58f9a6ff10e@mail.gmail.com> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.9; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4260 Lines: 98 On Wed, 27 Jan 2010 19:04:55 +0530 Balbir Singh wrote: > On Wed, Jan 27, 2010 at 6:45 PM, tip-bot for Anton Blanchard > wrote: > > Commit-ID: __43f85eb1411905afe5db510fbf9841b516e7e6a > > Gitweb: __ __ http://git.kernel.org/tip/43f85eab1411905afe5db510fbf9841b516e7e6a > > Author: __ __ Anton Blanchard > > AuthorDate: Mon, 18 Jan 2010 15:41:42 +1100 > > Committer: __Ingo Molnar > > CommitDate: Wed, 27 Jan 2010 08:34:38 +0100 > > > > sched: cpuacct: Use bigger percpu counter batch values for stats counters > > > > When CONFIG_VIRT_CPU_ACCOUNTING and CONFIG_CGROUP_CPUACCT are enabled we > > can call cpuacct_update_stats with values much larger than > > percpu_counter_batch. This means the call to percpu_counter_add will > > always add to the global count which is protected by a spinlock and we > > end up with a global spinlock in the scheduler. > > > > Based on an idea by KOSAKI Motohiro, this patch scales the batch value by > > cputime_one_jiffy such that we have the same batch limit as we would if > > CONFIG_VIRT_CPU_ACCOUNTING was disabled. His patch did this once at boot > > but that initialisation happened too early on PowerPC (before time_init) > > and it was never updated at runtime as a result of a hotplug cpu > > add/remove. > > > > This patch instead scales percpu_counter_batch by cputime_one_jiffy at > > runtime, which keeps the batch correct even after cpu hotplug operations. > > We cap it at INT_MAX in case of overflow. > > > > For architectures that do not support CONFIG_VIRT_CPU_ACCOUNTING, > > cputime_one_jiffy is the constant 1 and gcc is smart enough to optimise > > min(s32 percpu_counter_batch, INT_MAX) to just percpu_counter_batch at > > least on x86 and PowerPC. So there is no need to add an #ifdef. > > > > On a 64 thread PowerPC box with CONFIG_VIRT_CPU_ACCOUNTING and > > CONFIG_CGROUP_CPUACCT enabled, a context switch microbenchmark is 234x > > faster and almost matches a CONFIG_CGROUP_CPUACCT disabled kernel: > > > > CONFIG_CGROUP_CPUACCT disabled: __ __ __ __ 16906698 ctx switches/sec > > CONFIG_CGROUP_CPUACCT enabled: __ __ __ __ __ __ 61720 ctx switches/sec > > CONFIG_CGROUP_CPUACCT + patch: __ __ __ __ __16663217 ctx switches/sec > > > > Tested with: > > > > __wget http://ozlabs.org/~anton/junkcode/context_switch.c > > __make context_switch > > __for i in `seq 0 63`; do taskset -c $i ./context_switch & done > > __vmstat 1 > > > > Signed-off-by: Anton Blanchard > > Signed-off-by: Peter Zijlstra > > LKML-Reference: <20100118044142.GS12666@kryten> > > Signed-off-by: Ingo Molnar > > --- > > __kernel/sched.c | __ __4 +++- > > __1 files changed, 3 insertions(+), 1 deletions(-) > > > > diff --git a/kernel/sched.c b/kernel/sched.c > > index 3a8fb30..8f94138 100644 > > --- a/kernel/sched.c > > +++ b/kernel/sched.c > > @@ -10906,6 +10906,7 @@ static void cpuacct_update_stats(struct task_struct *tsk, > > __ __ __ __ __ __ __ __enum cpuacct_stat_index idx, cputime_t val) > > __{ > > __ __ __ __struct cpuacct *ca; > > + __ __ __ int batch; > > > > __ __ __ __if (unlikely(!cpuacct_subsys.active)) > > __ __ __ __ __ __ __ __return; > > @@ -10913,8 +10914,9 @@ static void cpuacct_update_stats(struct task_struct *tsk, > > __ __ __ __rcu_read_lock(); > > __ __ __ __ca = task_ca(tsk); > > > > + __ __ __ batch = min_t(long, percpu_counter_batch * cputime_one_jiffy, INT_MAX); > > __ __ __ __do { > > - __ __ __ __ __ __ __ percpu_counter_add(&ca->cpustat[idx], val); > > + __ __ __ __ __ __ __ __percpu_counter_add(&ca->cpustat[idx], val, batch); > > __ __ __ __ __ __ __ __ca = ca->parent; > > __ __ __ __} while (ca); > > __ __ __ __rcu_read_unlock(); ^^ your email client inexplicably fills emails with 0xa0 > IIRC, Andrew picked up this patch as well and applied some checkpatch > fixes too.. No, I have no changes. Last I heard, Anton was "working on a useful comment" and will be redoing the patch. -- 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/