linux-kernel - Re: [PATCH 1/7] perf: allow for PMU-specific event filtering

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Message-ID: <20150527085113.GV3644@twins.programming.kicks-ass.net>
Date:	Wed, 27 May 2015 10:51:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Mark Rutland <mark.rutland@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"acme@...nel.org" <acme@...nel.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"paulus@...ba.org" <paulus@...ba.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Drew Richardson <Drew.Richardson@....com>
Subject: Re: [PATCH 1/7] perf: allow for PMU-specific event filtering

On Fri, May 22, 2015 at 03:08:44PM +0100, Will Deacon wrote:
> Hi Mark,
> 
> On Wed, May 13, 2015 at 05:12:23PM +0100, Mark Rutland wrote:
> > In certain circumstances it may not be possible to schedule particular
> > events due to constraints other than a lack of hardware counters (e.g.
> > on big.LITTLE systems where CPUs support different events). The core
> > perf event code does not distinguish these cases and pessimistically
> > assumes that any failure to schedule an event means that it is not worth
> > attempting to schedule later events, even if some hardware counters are
> > still unused.
> > 
> > When an event a pmu cannot schedule exists in a flexible group list it
> > can unnecessarily prevent event groups following it in the list from
> > being scheduled (until it is rotated to the end of the list). This means
> > some events are scheduled for only a portion of the time they could be,
> > and for short running programs no events may be scheduled if the list is
> > initially sorted in an unfortunate order.
> > 
> > This patch adds a new (optional) filter_match function pointer to struct
> > pmu which a pmu driver can use to tell perf core when an event matches
> > pmu-specific scheduling requirements. This plugs into the existing
> > event_filter_match logic, and makes it possible to avoid the scheduling
> > problem described above. When no filter is provided by the PMU, the
> > existing behaviour is retained.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Acked-by: Will Deacon <will.deacon@....com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Paul Mackerras <paulus@...ba.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> > ---
> >  include/linux/perf_event.h | 5 +++++
> >  kernel/events/core.c       | 8 +++++++-
> >  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> Whilst I'm really keen to merge the architecture-specific parts of this
> series, I'm going to need an Ack from one of the perf core maintainers
> on this patch.
> 
> Peter, can you take a look please? (and I assume this is self-contained
> enough not to conflict heavily with the current perf queue?).

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Merge it however you like, but test merge against tip/perf/core or
something of that nature, if a conflict pops up, maybe keep this one
patch in a separate branch such that it can also be pulled into
tip/perf/core -- but as you say, I don't really suspect a conflict.
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