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Subject: Re: [RFC][PATCH] perf: sysfs type id
From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Eranian <eranian@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
        Lin Ming <ming.m.lin@intel.com>,
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Date: Wed, 10 Nov 2010 22:05:35 +0100
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On Wed, 2010-11-10 at 21:53 +0100, Stephane Eranian wrote:
> On Wed, Nov 10, 2010 at 9:32 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Wed, 2010-11-10 at 21:08 +0100, Stephane Eranian wrote:
> >> Would that be by passing the full filename to the tool?
> >
> > possible, or something like <pmu-name>:<event-name>, cpu:cycles would
> > map to /sys/class/pmu/cpu/events/cycles (given the previous patch).
> >
> >
> Ok, but I think you're proposal is missing one bit. You are addressing
> the class (or type) of PMU, but you are not addressing the naming of
> an instance.
> 
> Let's take an example, suppose you have counters on a graphic card.
> Your system has two such graphic cards. In your scheme you would
> end up with a sys/class/pmu/gfx/.....
> 
> But now, suppose I want to count cycles on the first graphic card.
> Seems to me you need to expose the instances as well. The instance
> number needs to be passed in the attr struct somehow.
> 
> You can either create multiple subdir under gfx, or have this info somewhere
> else in the sysfs tree, if people really care about class vs. instance.
> 
> I can see users doing:
> $ perf stat -e gfx@1::cycles ...  -> sys/class/gfx/1/event/cycles
> 
> The reason I am using :: here is because libpfm4 is already using
> this as a separator for PMU type vs. event.


right, so the idea is to have these pmu devices hooked into the existing
sysfs topology, my proposed patch misses that bit because I wanted to
get something out before having to dig through the topology code trying
to figure out how all that works.

So the 'cpu' pmu device would be linked from:

  /sys/devices/system/cpu/pmu -> /sys/class/pmu/cpu

and gfx things would be linked like:

  /sys/devices/pci0000:00/0000:00:1e.0/0000:0b:01.0/drm/card0/pmu -> /sys/class/pmu/radeon0


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