Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755639Ab0AREoG (ORCPT ); Sun, 17 Jan 2010 23:44:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753344Ab0AREoE (ORCPT ); Sun, 17 Jan 2010 23:44:04 -0500 Received: from ozlabs.org ([203.10.76.45]:51429 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751586Ab0AREoB (ORCPT ); Sun, 17 Jan 2010 23:44:01 -0500 Date: Mon, 18 Jan 2010 15:41:42 +1100 From: Anton Blanchard To: Bharata B Rao Cc: KOSAKI Motohiro , Ingo Molnar , Balbir Singh , mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, schwidefsky@de.ibm.com, balajirrao@gmail.com, dhaval@linux.vnet.ibm.com, tglx@linutronix.de, kamezawa.hiroyu@jp.fujitsu.com, akpm@linux-foundation.org, Tony Luck , Fenghua Yu , Heiko Carstens , linux390@de.ibm.com Subject: [PATCH] sched: cpuacct: Use bigger percpu counter batch values for stats counters Message-ID: <20100118044142.GS12666@kryten> References: <20090512102412.GG6351@balbir.in.ibm.com> <20090512102939.GB11714@elte.hu> <20090512193656.D647.A69D9226@jp.fujitsu.com> <20090716081010.GB3134@in.ibm.com> <20090716083948.GA2950@kryten> <20090820051038.GF21100@kryten> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090820051038.GF21100@kryten> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3274 Lines: 82 Hi, Another try at this percpu_counter batch issue with CONFIG_VIRT_CPU_ACCOUNTING and CONFIG_CGROUP_CPUACCT enabled. Thoughts? -- 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 --- Note: ccing ia64 and s390 who have not yet added code to statically initialise cputime_one_jiffy at boot. See a42548a18866e87092db93b771e6c5b060d78401 (cputime: Optimize jiffies_to_cputime(1) for details). Adding this would help optimise not only this patch but many other areas of the scheduler when CONFIG_VIRT_CPU_ACCOUNTING is enabled. Index: linux.trees.git/kernel/sched.c =================================================================== --- linux.trees.git.orig/kernel/sched.c 2010-01-18 14:27:12.000000000 +1100 +++ linux.trees.git/kernel/sched.c 2010-01-18 15:21:59.000000000 +1100 @@ -10894,6 +10894,7 @@ static void cpuacct_update_stats(struct enum cpuacct_stat_index idx, cputime_t val) { struct cpuacct *ca; + int batch; if (unlikely(!cpuacct_subsys.active)) return; @@ -10901,8 +10902,9 @@ static void cpuacct_update_stats(struct 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(); -- 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/