linux-kernel - Re: [PATCH v2 6/6] perf tool: Parse general/raw events from sysfs

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Date:	Sat, 6 Aug 2011 13:10:10 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 6/6] perf tool: Parse general/raw events from sysfs

Hi,

On Fri, Jul 15, 2011 at 7:35 AM, Lin Ming <ming.m.lin@...el.com> wrote:
> PMU can export general events to sysfs, for example,
>
> /sys/bus/event_source/devices/uncore/events
> └── cycle
>
> Then specify the event as <pmu>:<event>,
>
> $ sudo perf stat -a -C 0 -e uncore:cycle

I think this event syntax should be adjusted a bit.

How would the tool differentiate:
       perf stat -e uncore:cycle
form:
      perf stat -e cycle:u

It would have to scan sysfs for a 'cycle' PMU and conclude
there is none,  then resolve the 'cycle' event name. And if
you're unlucky and you have a event name that matches
the PMU name, you get into troubles.

I think, one could instead do:

    perf stat -e uncore::cycle:k

That way, by virtue of the '::' separator, the tool would know
that it needs to first look into sysfs for an 'uncore' PMU, then
it needs to look for the 'cycle' event.

I also use the '::' notation in libpfm4 to separate the PMU model
form the event+umask+modifiers.

I also suspect that with this sysfs interface for PMU models, you
would simply add a number to differentiate each instance of a PMU.
So for GPU, you would do:
    perf stat -e  gfx0::cycles

Is that right?
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