Commit-ID: 43f85eab1411905afe5db510fbf9841b516e7e6a Gitweb: http://git.kernel.org/tip/43f85eab1411905afe5db510fbf9841b516e7e6a Author: Anton Blanchard <anton@xxxxxxxxx> AuthorDate: Mon, 18 Jan 2010 15:41:42 +1100 Committer: Ingo Molnar <mingo@xxxxxxx> 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 <anton@xxxxxxxxx> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> LKML-Reference: <20100118044142.GS12666@kryten> Signed-off-by: Ingo Molnar <mingo@xxxxxxx> --- 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(); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html