Re: [RFC 04/10] drm/i915: Expose a PMU interface for perf queries

From: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
To: "peterz@infradead.org" <peterz@infradead.org>
Cc: "Intel-gfx@lists.freedesktop.org" <Intel-gfx@lists.freedesktop.org>
Subject: Re: [RFC 04/10] drm/i915: Expose a PMU interface for perf queries
Date: Wed, 23 Aug 2017 18:40:02 +0000	[thread overview]
Message-ID: <1503484676.5383.38.camel@intel.com> (raw)
In-Reply-To: <20170823180134.3ufier7vsok6itew@hirez.programming.kicks-ass.net>

On Wed, 2017-08-23 at 20:01 +0200, Peter Zijlstra wrote:
> On Wed, Aug 23, 2017 at 05:51:38PM +0000, Rogozhkin, Dmitry V wrote:
> 
> > https://patchwork.freedesktop.org/patch/171953/. This patch makes 'perf
> > stat -e i915/rcs0-busy/' to error out and supports 'perf stat -e
> > i915/rcs0-busy/ -a -C0'. I still think I miss something since 'perf stat
> > -e i915/rcs0-busy/ -a' will give metrics multiplied by number of active
> > CPUs, but that's look closer to what is needed.
> 
> IIRC an uncore PMU should expose a cpumask through sysfs, and then perf
> tools will read that mask and auto-magically limit the number of CPUs it
> instantiates the counter on.
> 
> See for instance arch/x86/events/intel/cstate.c, that is a fairly
> trivial uncore PMU, look for "DEVICE_ATTR(cpumask".

Thank you for the reference! I will go forward and try to implement this
for i915 PMU.

> 
> For example, on my 2 socket 10 core ivb-ep:
> 
> root@ivb-ep:~# cat /sys/bus/event_source/devices/cstate_pkg/cpumask
> 0,10
> 

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