linux-kernel - Re: [PATCH v9 12/14] x86: perf: intel

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Date:	Mon, 26 Jan 2015 17:55:36 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, markus.t.metzger@...el.com,
	mathieu.poirier@...aro.org, Kaixu Xia <kaixu.xia@...aro.org>,
	acme@...radead.org
Subject: Re: [PATCH v9 12/14] x86: perf: intel_pt: Intel PT PMU driver

On Tue, Jan 20, 2015 at 03:20:00PM +0200, Alexander Shishkin wrote:
> > As for the exclusive events, how about something like the code below (on
> > top of the previous exclusive event patch)? The only remaining issue
> > that I see is creating cpu-wide events in the presence of per-thread
> > (event->cpu==-1) events. Both would still work, but only one of them
> > will actually get scheduled at a time. I'm thinking about adding a
> > counter for per-thread events to struct pmu for this purpose, so that if
> > any are present, we can disallow creating cpu-wide events. Or, we can
> > leave it as it is.
> >
> > What do you think?
> >
> > ---
> >  kernel/events/core.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 47 insertions(+), 5 deletions(-)
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index cf0bf99f53..e8c86530e2 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -7688,14 +7688,11 @@ static bool exclusive_event_match(struct perf_event *e1, struct perf_event *e2)
> >  	return false;
> >  }
> >  
> > -static bool exclusive_event_ok(struct perf_event *event,
> > -			      struct perf_event_context *ctx)
> > +static bool __exclusive_event_ok(struct perf_event *event,
> > +				 struct perf_event_context *ctx)
> >  {
> >  	struct perf_event *iter_event;
> >  
> > -	if (!(event->pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
> > -		return true;
> > -
> >  	list_for_each_entry(iter_event, &ctx->event_list, event_entry) {
> >  		if (exclusive_event_match(iter_event, event))
> >  			return false;
> > @@ -7704,6 +7701,51 @@ static bool exclusive_event_ok(struct perf_event *event,
> >  	return true;
> >  }
> >  
> > +static bool __exclusive_event_ok_on_cpu(struct perf_event *event, int cpu)
> > +{
> > +	struct perf_event_context *cpuctx;
> > +	bool ret;
> > +
> > +	cpuctx = find_get_context(event->pmu, NULL, cpu);
> > +	mutex_lock(&cpuctx->mutex);
> > +	ret = __exclusive_event_ok(event, cpuctx);
> > +	perf_unpin_context(cpuctx);
> > +	put_ctx(cpuctx);
> > +	mutex_unlock(&cpuctx->mutex);
> 
> Actually, find_get_context() is not needed here, the following should be
> sufficient:
> 
> 	cpuctx = &per_cpu_ptr(event->pmu->pmu_cpu_context, cpu)->ctx;
> 
> 	mutex_lock(&cpuctx->mutex);
> 	ret = __exclusive_event_ok(event, cpuctx);
> 	mutex_unlock(&cpuctx->mutex);

Yes that'll work.
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