From: Anton Blanchard Date: Tue, 2 Feb 2010 22:46:13 +0000 (-0800) Subject: sched: cpuacct: Use bigger percpu counter batch values for stats counters X-Git-Tag: v2.6.34-rc1~260^2~4 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fa535a77bd3fa32b9215ba375d6a202fe73e1dd6;p=pandora-kernel.git 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 Reviewed-by: KOSAKI Motohiro Acked-by: Balbir Singh Tested-by: Balbir Singh Cc: Peter Zijlstra Cc: Martin Schwidefsky Cc: "Luck, Tony" Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed