Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters

Balbir Singh
2009-05-12T10:11:19Z

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2009-05-12 19:01:25]:

> >
> > * tip-bot for KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> >
> > > Commit-ID: 50fbed3bb72cbe38a665512771a91a96d028de46
> > > Gitweb: http://git.kernel.org/tip/50fbed3bb72cbe38a665512771a91a96d028de46
> > > Author: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > > AuthorDate: Sat, 9 May 2009 19:14:58 +0900
> > > Committer: Ingo Molnar <mingo@elte.hu>
> > > CommitDate: Mon, 11 May 2009 14:32:57 +0200
> > >
> > > sched: cpuacct: Use bigger percpu counter batch values for stats counters
> >
> > -tip testing found a build failure with this patch:
> >
> > kernel/sched.c:9278: error: ?$B!Fpercpu_counter_batch?$B!G undeclared (first use in this function)
> > kernel/sched.c:9278: error: (Each undeclared identifier is reported only once
> > kernel/sched.c:9278: error: for each function it appears in.)
>
> Oh, my fault again. Good catch!
>
>
>
> Changelog:
> since V5
> - fix build error when UP
>
> since V4
> - move cpuacct_batch initialization into sched_init()
>
> since V3
> - rewirte patch description (thanks Bharata!)
> - append read_mostly to cpuacct_batch
> - cpuacct_batch is initialized by sched_init()
>
> since v2
> - revert using percpu_counter_sum()
>
> since v1
> - use percpu_counter_sum() instead percpu_counter_read()
>
>
> ---------------------------------------------------------
> Subject: [PATCH v6] cpuacct: Use bigger percpu counter batch values for stats counters on archs that have VIRT_CPU_ACCOUNTING=y
>
> percpu counters used to accumulate statistics in cpuacct controller use
> the default batch value [max(2*nr_cpus, 32)] which can be too small for
> archs that define VIRT_CPU_ACCOUNTING. In such archs, a tick could result in
> cputime updates in the range of thousands. As a result, cpuacct_update_stats()
> would end up acquiring the percpu counter spinlock on every tick which
> is not good for performance.
>
> Let those architectures to have a bigger batch threshold so that percpu counter
> spinlock isn't taken on every tick. This change doesn't affect the archs which
> don't define VIRT_CPU_ACCOUNTING and they continue to have the default
> percpu counter batch value.
>
> Cc: Balaji Rao <balajirrao@gmail.com>
> Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> ---
> kernel/sched.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> Index: b/kernel/sched.c
> ===================================================================
> --- a/kernel/sched.c 2009-05-12 13:12:59.000000000 +0900
> +++ b/kernel/sched.c 2009-05-12 13:28:53.000000000 +0900
> @@ -870,6 +870,8 @@ static __read_mostly int scheduler_runni
> */
> int sysctl_sched_rt_runtime = 950000;
>
> +static __read_mostly s32 cpuacct_batch;
> +
> static inline u64 global_rt_period(void)
> {
> return (u64)sysctl_sched_rt_period * NSEC_PER_USEC;
> @@ -9284,6 +9286,10 @@ void __init sched_init(void)
>
> perf_counter_init();
>
> +#ifdef CONFIGCONFIG_SMP
> + cpuacct_batch = jiffies_to_cputime(percpu_counter_batch);
> +#endif

Slow down and compile patches before sending them out.. please. That
is a basic expectation if you expect it to be merged.

--
Balbir