linux-kernel - Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering

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Date:	Fri, 11 Dec 2015 14:23:36 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	vince@...ter.net, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering

On Fri, Dec 11, 2015 at 03:02:01PM +0100, Peter Zijlstra wrote:
> On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
> 
> > The pmu driver interface basically adds an extra callback to the
> > pmu driver structure, which validates the filter configuration proposed
> > by the user against what the hardware is actually capable of doing
> > and translates it into something that pmu::start can program into
> > hardware.
> 
> > @@ -388,12 +393,38 @@ struct pmu {
> >  	void (*free_aux)		(void *aux); /* optional */
> >  
> >  	/*
> > +	 * Validate instruction tracing filters: make sure hw supports the
> > +	 * requested configuration and number of filters.
> > +	 *
> > +	 * Configure instruction tracing filters: translate hw-agnostic filter
> > +	 * into hardware configuration in event::hw::itrace_filters
> > +	 */
> > +	int (*itrace_filter_setup)	(struct perf_event *event); /* optional */
> > +
> > +	/*
> >  	 * Filter events for PMU-specific reasons.
> >  	 */
> >  	int (*filter_match)		(struct perf_event *event); /* optional */
> >  };
> 
> Any reason you cannot use pmu::filter_match ?

Maybe I've misunderstood your point, but the two seem quite different.

We introduced pmu::filter_match to apply a SW filter each time we
installed events from a context. We use that on ARM to avoid programming
big events into little cores and vice-versa.

As far as I can see, itrace_filter_setup is closer in operation to
event_init. It can fail at configuration time (long before scheduling
events to cores), and leaves the actual filtering to the HW.

Thanks,
Mark.
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