linux-kernel - Re: [PATCH v5 2/2] arm: perf: Add event descriptions

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Date:	Thu, 15 Oct 2015 16:42:52 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Pawel Moll <pawel.moll@....com>
Cc:	Drew Richardson <drew.richardson@....com>,
	Will Deacon <will.deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Wade Cherry <Wade.Cherry@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 2/2] arm: perf: Add event descriptions

On Thu, Oct 15, 2015 at 04:20:37PM +0100, Pawel Moll wrote:
> On Thu, 2015-10-15 at 08:15 -0700, Drew Richardson wrote:
> > On Thu, Oct 15, 2015 at 02:21:12PM +0100, Will Deacon wrote:
> > > On Tue, Oct 13, 2015 at 08:36:45AM -0700, Drew Richardson wrote:
> > > > Add additional information about the ARM architected hardware events
> > > > to make counters self describing. This makes the hardware PMUs easier
> > > > to use as perf list contains possible events instead of users having
> > > > to refer to documentation like the ARM TRMs.
> > > > 
> > > > Signed-off-by: Drew Richardson <drew.richardson@....com>
> > > > ---
> > > >  arch/arm/kernel/perf_event_v7.c | 121 ++++++++++++++++++++++++++++++++++++++++
> > > >  drivers/perf/arm_pmu.c          |   1 +
> > > >  2 files changed, 122 insertions(+)
> > > 
> > > [...]
> > > 
> > > > diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> > > > index 2365a32a595e..e933d2dd71c0 100644
> > > > --- a/drivers/perf/arm_pmu.c
> > > > +++ b/drivers/perf/arm_pmu.c
> > > > @@ -548,6 +548,7 @@ static void armpmu_init(struct arm_pmu *armpmu)
> > > >  		.stop		= armpmu_stop,
> > > >  		.read		= armpmu_read,
> > > >  		.filter_match	= armpmu_filter_match,
> > > > +		.attr_groups	= armpmu->pmu.attr_groups,
> > > 
> > > I don't understand this hunk. What's it doing?
> > 
> > I'm not 100% clear either on what it's doing. But without this line
> > the attr_groups don't get passed on and I don't see them on my TC2. I
> > debugged the issue down to this but it may not be the proper way to
> > solve the problem.
> 
> The perf core creates attributes passed as pmu.attr_groups
> in /sys/bus/events/devices/<pmu>.

Sure, but the confusion here had to do with why we were re-assigning the
field to itself rather than what the purpose of said field was.

Thanks,
Mark.
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