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

[Peter Zijlstra]

On Wed, Aug 23, 2017 at 06:38:05PM +0000, Rogozhkin, Dmitry V wrote:
> On Wed, 2017-08-23 at 20:04 +0200, Peter Zijlstra wrote:
> > On Wed, Aug 23, 2017 at 05:51:38PM +0000, Rogozhkin, Dmitry V wrote:
> > 
> > > > The above command tries to add an event 'i915/rcs0-busy/' to a task. How
> > > > are i915 resource associated to any one particular task?
> > > 
> > > Currently in no way, they are global.
> > 
> > Right. So no per DRM context things. Can you have multiple DRM contexts
> > per task? If so that would make things slightly tricky when you get away
> > from !global counters.
> 
> Just to be sure we are on the same page: under task we understand the
> process which is being monitored with the perf: "perf stat -e <ev>
> task.sh"? Yes, each process may have few DRM contexts, so we are in a
> tricky space:).

task is really what userspace calls a thread.

> If we will decide to support per-task counters in the future, would it
> be possible to preserve global mode providing end-user a choice: monitor
> per-process or globally?

Of course, we could even do a whole new PMU for possible finer grained
stuff.