linux-kernel - Re: [PATCH 06/14] perf, core: always switch pmu specific data during context switch

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Message-ID: <CABPqkBQS=kSyRb0hb7DSTAOmUpB03_Cq70Wi1NvHj+DAQc4FVQ@mail.gmail.com>
Date:	Wed, 5 Feb 2014 18:19:27 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 06/14] perf, core: always switch pmu specific data during
 context switch

On Fri, Jan 3, 2014 at 6:48 AM, Yan, Zheng <zheng.z.yan@...el.com> wrote:
> If two tasks were both forked from the same parent task, Events in their perf
> task contexts can be the same. Perf core optimizes context switch oout in this
> case.
>
> Previous patch inroduces pmu specific data. The data is task specific, so we
> should switch the data even when context switch is optimized out.
>
Reviwed-by: Stephane Eranian <eranian@...gle.com>
> Signed-off-by: Yan, Zheng <zheng.z.yan@...el.com>
> ---
>  kernel/events/core.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b6650ab..d6d8dea 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2319,6 +2319,8 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
>                         next->perf_event_ctxp[ctxn] = ctx;
>                         ctx->task = next;
>                         next_ctx->task = task;
> +                       ctx->task_ctx_data = xchg(&next_ctx->task_ctx_data,
> +                                                 ctx->task_ctx_data);
>                         do_switch = 0;
>
>                         perf_event_sync_stat(ctx, next_ctx);
> --
> 1.8.4.2
>
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