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Date: Fri, 16 Oct 2015 12:33:45 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Robert Bragg <robert@sixbynine.org>, intel-gfx@lists.freedesktop.org,
        Daniel Vetter <daniel.vetter@intel.com>,
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Subject: Re: [RFC 0/6] Non perf based Gen Graphics OA unit driver
Message-ID: <20151016103345.GS3816@twins.programming.kicks-ass.net>
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On Fri, Oct 16, 2015 at 12:02:28PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > > - We may be making some technical compromises a.t.m for the sake of
> > >   using perf.
> > > 
> > >     perf_event_open() requires events to either relate to a pid or a
> > >     specific cpu core, while our device pmu relates to neither.  Events
> > >     opened with a pid will be automatically enabled/disabled according
> > >     to the scheduling of that process - so not appropriate for us.
> > 
> > Right; the traditional cpu/pid mapping doesn't work well for devices;
> > but maybe, with some work, we can create something like that
> > global/local render context from it; although I've no clue what form
> > that would need at this time.
> 
> Could someone please help with some very basic questions, such as what the 
> hardware model of the 'OA' unit model is? How are OA registers set up, how are 
> their values made accessible to the host side, etc.

Robert linked to:

  https://01.org/sites/default/files/documentation/observability_performance_counters_haswell.pdf

In a previous posting. It has some info, but full documentation, is as
per the initial post, 'pending'.