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

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Message-ID: <20131216110728.GW21999@twins.programming.kicks-ass.net>
Date:	Mon, 16 Dec 2013 12:07:28 +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 Mon, Dec 16, 2013 at 01:00:36PM +0200, Alexander Shishkin wrote:
> Peter Zijlstra <peterz@...radead.org> writes:
> 
> > 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.
> 
> Well, given the disable_count check in perf_pmu_{en,dis}able, this one
> indeed looks redundant to me. Should I resend this one separately?

Yes, it seems an unrelated bugfix, like Andi said.
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