linux-kernel - Re: [PATCH] sched/cputime: Mitigate performance regression in times()/clock

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Message-ID: <20160802103729.GG6862@twins.programming.kicks-ass.net>
Date:	Tue, 2 Aug 2016 12:37:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Giovanni Gherdovich <ggherdovich@...e.cz>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Mike Galbraith <mgalbraith@...e.de>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.com>
Subject: Re: [PATCH] sched/cputime: Mitigate performance regression in
 times()/clock_gettime()

On Tue, Jul 26, 2016 at 04:07:14PM +0200, Giovanni Gherdovich wrote:

> Signed-off-by: Mike Galbraith <mgalbraith@...e.de>
> Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>

SoB chain is borken. Either Mike wrote the patch in which case you're
missing a From: Mike header someplace, or you wrote it and Mike needs to
be a Ack/Reviewed or somesuch.

> ---
>  kernel/sched/core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 51d7105..0ef1e69 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2998,6 +2998,10 @@ unsigned long long task_sched_runtime(struct task_struct *p)
>  	 * thread, breaking clock_gettime().
>  	 */
>  	if (task_current(rq, p) && task_on_rq_queued(p)) {
> +#if defined(CONFIG_FAIR_GROUP_SCHED)

This here wants a comment on why we're doing this. Because I'm sure that
if someone were to read this code in a few weeks they'd go WTF!?

Also, is there a possibility of manual CSE we should do?

> +		prefetch((&p->se)->cfs_rq->curr);
> +		prefetch(&(&p->se)->cfs_rq->curr->exec_start);
> +#endif
>  		update_rq_clock(rq);
>  		p->sched_class->update_curr(rq);
>  	}
> -- 
> 2.6.6
>