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

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Date:	Tue, 12 May 2009 15:40:57 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	schwidefsky@...ibm.com, balajirrao@...il.com,
	dhaval@...ux.vnet.ibm.com, bharata@...ux.vnet.ibm.com,
	tglx@...utronix.de, kamezawa.hiroyu@...fujitsu.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter
	batch values for stats counters

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

> > 
> > * tip-bot for KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> > 
> > > Commit-ID:  50fbed3bb72cbe38a665512771a91a96d028de46
> > > Gitweb:     http://git.kernel.org/tip/50fbed3bb72cbe38a665512771a91a96d028de46
> > > Author:     KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > > AuthorDate: Sat, 9 May 2009 19:14:58 +0900
> > > Committer:  Ingo Molnar <mingo@...e.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@...il.com>
> Cc: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...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
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