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

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Message-ID: <CABPqkBTp_R6RRUdkYwB5O6HN6i05V=4eV3Pb2NaS3KZUhBN7fg@mail.gmail.com>
Date:	Sun, 7 Aug 2011 16:47:27 -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

On Sat, Aug 6, 2011 at 4:38 PM, Lin Ming <ming.m.lin@...el.com> wrote:
> 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.
>
Well, there is something I am still missing here.

Based on the current patch, it seems that each instance
of a PMU needs to register to get an ID and an entry in
sysfs.

Suppose you have a system with two graphics cards. Then,
you would need two IDs and two entries in sysfs to correctly
name each gfx card.

That means that the kernel would have to iterate over each instance
of a PMU and create a name for it, e.g., something like:
   for_each_gfx_card(i) {
       sprintf(name, "gfx%d", i);
      register_pmu(&pmu, name);
  }

Is that what you are proposing?
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