Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754153Ab3F0Tz4 (ORCPT ); Thu, 27 Jun 2013 15:55:56 -0400 Received: from e23smtp02.au.ibm.com ([202.81.31.144]:42522 "EHLO e23smtp02.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752933Ab3F0Tzy (ORCPT ); Thu, 27 Jun 2013 15:55:54 -0400 From: "Srivatsa S. Bhat" Subject: [PATCH v3 00/45] CPU hotplug: stop_machine()-free CPU hotplug, part 1 To: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, walken@google.com, vincent.guittot@linaro.org, laijs@cn.fujitsu.com, David.Laight@aculab.com Cc: rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, sbw@mit.edu, fweisbec@gmail.com, zhong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 28 Jun 2013 01:22:26 +0530 Message-ID: <20130627195136.29830.10445.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13062719-5490-0000-0000-000003BA3082 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10530 Lines: 207 Hi, This patchset is a first step towards removing stop_machine() from the CPU hotplug offline path. It introduces a set of APIs (as a replacement to preempt_disable()/preempt_enable()) to synchronize with CPU hotplug from atomic contexts. The motivation behind getting rid of stop_machine() is to avoid its ill-effects, such as performance penalties[1] and the real-time latencies it inflicts on the system (and also things involving stop_machine() have often been notoriously hard to debug). And in general, getting rid of stop_machine() from CPU hotplug also greatly enhances the elegance of the CPU hotplug design itself. Getting rid of stop_machine() involves building the corresponding infrastructure in the core CPU hotplug code and converting all places which used to depend on the semantics of stop_machine() to synchronize with CPU hotplug. This patchset builds a first-level base infrastructure on which tree-wide conversions can be built upon, and also includes the conversions themselves. We certainly need a few more careful tree-sweeps to complete the conversion, but the goal of this patchset is to introduce the core pieces and to get the first batch of conversions in, while covering a reasonable bulk among them. This patchset also has a debug infrastructure to help with the conversions - with the newly introduced CONFIG_DEBUG_HOTPLUG_CPU option turned on, it prints warnings whenever the need for a conversion is detected. Patches 4-7 build this framework. Needless to say, I'd really appreciate if people could test kernels with this option turned on and report omissions or better yet, send patches to contribute to this effort. [It is to be noted that this patchset doesn't replace stop_machine() yet, so the immediate risk in having an unconverted (or converted) call-site is nil, since there is no major functional change involved.] Once the conversion gets completed, we can finalize on the design of the stop_machine() replacement and use that in the core CPU hotplug code. We have had some discussions in the past where we debated several different designs[2]. We'll revisit that with more ideas once this conversion gets over. This patchset applies on current tip:master. It is also available in the following git branch: git://github.com/srivatsabhat/linux.git stop-mch-free-cpuhp-part1-v3 Thank you very much! Changes in v3: ------------- * Added _nocheck() variants of cpu accessor functions for use in RCU and percpu-counter code. Reworked the RCU and percpu-counter patches accordingly. * Dropped the patch related to kvm-vmx, since it was unnecessary. * Added changes to r4k_on_each_cpu() in Mips, as pointed out by Ralf Baechle. * Added Acks and rebased to current tip/master. Changes in v2: ------------- * Build-fix for !HOTPLUG_CPU case. * Minor code cleanups, and added a few comments. References: ---------- 1. Performance difference between CPU Hotplug with and without stop_machine(): http://article.gmane.org/gmane.linux.kernel/1435249 2. Links to discussions around alternative synchronization schemes to replace stop_machine() in the CPU Hotplug code: v6: http://lwn.net/Articles/538819/ v5: http://lwn.net/Articles/533553/ v4: https://lkml.org/lkml/2012/12/11/209 v3: http://lwn.net/Articles/528541/ v2: https://lkml.org/lkml/2012/12/5/322 v1: https://lkml.org/lkml/2012/12/4/88 http://lwn.net/Articles/527988/ 3. Links to previous versions of this patchset: v2: http://thread.gmane.org/gmane.linux.kernel/1515396 v1: http://lwn.net/Articles/556138/ -- Srivatsa S. Bhat (45): CPU hotplug: Provide APIs to prevent CPU offline from atomic context CPU hotplug: Clarify the usage of different synchronization APIs Documentation, CPU hotplug: Recommend usage of get/put_online_cpus_atomic() CPU hotplug: Add infrastructure to check lacking hotplug synchronization CPU hotplug: Protect set_cpu_online() to avoid false-positives CPU hotplug: Sprinkle debugging checks to catch locking bugs CPU hotplug: Add _nocheck() variants of accessor functions CPU hotplug: Expose the new debug config option CPU hotplug: Convert preprocessor macros to static inline functions smp: Use get/put_online_cpus_atomic() to prevent CPU offline sched/core: Use get/put_online_cpus_atomic() to prevent CPU offline migration: Use raw_spin_lock/unlock since interrupts are already disabled sched/fair: Use get/put_online_cpus_atomic() to prevent CPU offline timer: Use get/put_online_cpus_atomic() to prevent CPU offline sched/rt: Use get/put_online_cpus_atomic() to prevent CPU offline rcu: Use cpu_is_offline_nocheck() to avoid false-positive warnings tick-broadcast: Use get/put_online_cpus_atomic() to prevent CPU offline time/clocksource: Use get/put_online_cpus_atomic() to prevent CPU offline softirq: Use get/put_online_cpus_atomic() to prevent CPU offline irq: Use get/put_online_cpus_atomic() to prevent CPU offline net: Use get/put_online_cpus_atomic() to prevent CPU offline block: Use get/put_online_cpus_atomic() to prevent CPU offline percpu_counter: Use _nocheck version of for_each_online_cpu() infiniband: ehca: Use get/put_online_cpus_atomic() to prevent CPU offline [SCSI] fcoe: Use get/put_online_cpus_atomic() to prevent CPU offline staging/octeon: Use get/put_online_cpus_atomic() to prevent CPU offline x86: Use get/put_online_cpus_atomic() to prevent CPU offline perf/x86: Use get/put_online_cpus_atomic() to prevent CPU offline KVM: Use get/put_online_cpus_atomic() to prevent CPU offline x86/xen: Use get/put_online_cpus_atomic() to prevent CPU offline alpha/smp: Use get/put_online_cpus_atomic() to prevent CPU offline blackfin/smp: Use get/put_online_cpus_atomic() to prevent CPU offline cris/smp: Use get/put_online_cpus_atomic() to prevent CPU offline hexagon/smp: Use get/put_online_cpus_atomic() to prevent CPU offline ia64: irq, perfmon: Use get/put_online_cpus_atomic() to prevent CPU offline ia64: smp, tlb: Use get/put_online_cpus_atomic() to prevent CPU offline m32r: Use get/put_online_cpus_atomic() to prevent CPU offline MIPS: Use get/put_online_cpus_atomic() to prevent CPU offline mn10300: Use get/put_online_cpus_atomic() to prevent CPU offline powerpc, irq: Use GFP_ATOMIC allocations in atomic context powerpc: Use get/put_online_cpus_atomic() to prevent CPU offline powerpc: Use get/put_online_cpus_atomic() to avoid false-positive warning sh: Use get/put_online_cpus_atomic() to prevent CPU offline sparc: Use get/put_online_cpus_atomic() to prevent CPU offline tile: Use get/put_online_cpus_atomic() to prevent CPU offline Documentation/cpu-hotplug.txt | 20 +++- arch/alpha/kernel/smp.c | 19 ++- arch/blackfin/mach-common/smp.c | 4 - arch/cris/arch-v32/kernel/smp.c | 5 + arch/hexagon/kernel/smp.c | 3 + arch/ia64/kernel/irq_ia64.c | 15 +++ arch/ia64/kernel/perfmon.c | 8 + arch/ia64/kernel/smp.c | 12 +- arch/ia64/mm/tlb.c | 4 - arch/m32r/kernel/smp.c | 16 +-- arch/mips/kernel/cevt-smtc.c | 7 + arch/mips/kernel/smp.c | 16 +-- arch/mips/kernel/smtc.c | 12 ++ arch/mips/mm/c-octeon.c | 4 - arch/mips/mm/c-r4k.c | 5 + arch/mn10300/mm/cache-smp.c | 3 + arch/mn10300/mm/tlb-smp.c | 17 ++- arch/powerpc/kernel/irq.c | 9 +- arch/powerpc/kernel/machine_kexec_64.c | 4 - arch/powerpc/kernel/smp.c | 4 + arch/powerpc/kvm/book3s_hv.c | 5 + arch/powerpc/mm/mmu_context_nohash.c | 3 + arch/powerpc/oprofile/cell/spu_profiler.c | 3 + arch/powerpc/oprofile/cell/spu_task_sync.c | 4 + arch/powerpc/oprofile/op_model_cell.c | 6 + arch/sh/kernel/smp.c | 12 +- arch/sparc/kernel/smp_64.c | 12 +- arch/tile/kernel/module.c | 3 + arch/tile/kernel/tlb.c | 15 +++ arch/tile/mm/homecache.c | 3 + arch/x86/kernel/apic/io_apic.c | 21 +++- arch/x86/kernel/cpu/mcheck/therm_throt.c | 4 - arch/x86/kernel/cpu/perf_event_intel_uncore.c | 6 + arch/x86/mm/tlb.c | 14 +-- arch/x86/xen/mmu.c | 9 +- block/blk-softirq.c | 3 + drivers/infiniband/hw/ehca/ehca_irq.c | 5 + drivers/scsi/fcoe/fcoe.c | 7 + drivers/staging/octeon/ethernet-rx.c | 3 + include/linux/cpu.h | 29 +++++ include/linux/cpumask.h | 118 +++++++++++++++++++++ kernel/cpu.c | 138 +++++++++++++++++++++++++ kernel/irq/manage.c | 7 + kernel/irq/proc.c | 3 + kernel/rcutree.c | 12 ++ kernel/sched/core.c | 27 ++++- kernel/sched/fair.c | 14 ++- kernel/sched/rt.c | 14 +++ kernel/smp.c | 52 +++++---- kernel/softirq.c | 3 + kernel/time/clocksource.c | 5 + kernel/time/tick-broadcast.c | 8 + kernel/timer.c | 4 + lib/Kconfig.debug | 8 + lib/cpumask.c | 8 + lib/percpu_counter.c | 9 +- net/core/dev.c | 9 +- virt/kvm/kvm_main.c | 8 + 58 files changed, 674 insertions(+), 127 deletions(-) Regards, Srivatsa S. 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