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

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Date:	Sun, 07 Aug 2011 07:38:08 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Stephane Eranian <eranian@...gle.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

On Sun, 2011-08-07 at 04:10 +0800, Stephane Eranian wrote:
> 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.

Yes, I like this '::' separator too.
Will update to use it.

> 
> 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?

A number or other thing is OK.
 
int perf_pmu_register(struct pmu *pmu, char *name, int type)
will be called to register a PMU.

So I think any name that can differentiate each instance is OK.

Adding a number looks like the easiest way.

Thanks,
Lin Ming


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