Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754815Ab0A0Ne6 (ORCPT ); Wed, 27 Jan 2010 08:34:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754497Ab0A0Ne5 (ORCPT ); Wed, 27 Jan 2010 08:34:57 -0500 Received: from mail-px0-f182.google.com ([209.85.216.182]:51604 "EHLO mail-px0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752221Ab0A0Ne4 convert rfc822-to-8bit (ORCPT ); Wed, 27 Jan 2010 08:34:56 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=BINXHtVsACZel+SXhhZwJZ3teyEzCfGcCbmoBg1pSAEcztn9vv/e7jpKzw9WkLUbPV 5gPI4p4dA/mNUnQ+gGvXZE4ix45xSsHbJLXVRuGvfoZhgYtH+Z+7JV31WrVNsGw+D0xz vkfGa6Gw733ahQh77z35khg2MaNs2bxtEgO9k= MIME-Version: 1.0 In-Reply-To: References: <20100118044142.GS12666@kryten> Date: Wed, 27 Jan 2010 19:04:55 +0530 X-Google-Sender-Auth: 7428219a1903c633 Message-ID: <661de9471001270534ve6f7bf0nb58ef58f9a6ff10e@mail.gmail.com> Subject: Re: [tip:sched/urgent] sched: cpuacct: Use bigger percpu counter batch values for stats counters From: Balbir Singh To: 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, akpm@linux-foundation.org Cc: linux-tip-commits@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3751 Lines: 89 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(); IIRC, Andrew picked up this patch as well and applied some checkpatch fixes too.. Balbir -- 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/