linux-kernel - Re: [PATCH v0 01/71] perf: Disable all pmus on unthrottling and rescheduling

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Date:	Fri, 13 Dec 2013 19:06:38 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v0 01/71] perf: Disable all pmus on unthrottling and
 rescheduling

On Wed, Dec 11, 2013 at 02:36:13PM +0200, Alexander Shishkin wrote:
> Currently, only one pmu in a context gets disabled during unthrottling
> and event_sched_{out,in}, however, events in one context may belong to
> different pmus, which results in pmus being reprogrammed while they are
> still enabled. This patch temporarily disables pmus that correspond to
> each event in the context while these events are being modified.
> 
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> ---
>  kernel/events/core.c | 27 ++++++++++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 403b781..d656cd6 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1396,6 +1396,9 @@ event_sched_out(struct perf_event *event,
>  	if (event->state != PERF_EVENT_STATE_ACTIVE)
>  		return;
>  
> +	if (event->pmu != ctx->pmu)
> +		perf_pmu_disable(event->pmu);
> +
>  	event->state = PERF_EVENT_STATE_INACTIVE;
>  	if (event->pending_disable) {
>  		event->pending_disable = 0;
> @@ -1412,6 +1415,9 @@ event_sched_out(struct perf_event *event,
>  		ctx->nr_freq--;
>  	if (event->attr.exclusive || !cpuctx->active_oncpu)
>  		cpuctx->exclusive = 0;
> +
> +	if (event->pmu != ctx->pmu)
> +		perf_pmu_enable(event->pmu);
>  }
>  
>  static void

Hmm, indeed. Does it make sense to drop the conditional?
perf_pmu_{en,dis}able() is recursive and the thinking is that if its the
same PMU the cacheline is hot because we touched it already recently
anyway, so the unconditional inc/dec might actually be faster.. dunno.

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