On Wed, Jan 27, 2010 at 6:45 PM, tip-bot for Anton Blanchard <anton@xxxxxxxxx> wrote: > Commit-ID: 43f85eb1411905afe5db510fbf9841b516e7e6a > 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(); 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-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html