[Intel-gfx] [PATCH] drm/i915/selftests: Wait until we start timeslicing after a submit

[Chris Wilson]

Quoting Ruhl, Michael J (2020-04-03 21:31:42)
> >-----Original Message-----
> >From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Chris
> >Wilson
> >Sent: Friday, April 3, 2020 3:02 PM
> >To: intel-gfx at lists.freedesktop.org
> >Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >Subject: [Intel-gfx] [PATCH] drm/i915/selftests: Wait until we start timeslicing
> >after a submit
> >
> >If we submit, we do not start timeslicnig until we process the CS event
> 
> s/timeslicnig/timeslicing/
> 
> >that marks the start of the context running on HW. So in the selftest,
> >be sure to wait until we have processed the pending events before
> >asserting that timeslicing has begun.
> >
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >---
> > drivers/gpu/drm/i915/gt/selftest_lrc.c | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> >diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> >b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> >index 985d4041d929..9e02917695b1 100644
> >--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> >+++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> >@@ -1244,7 +1244,11 @@ static int live_timeslice_queue(void *arg)
> >               if (err)
> >                       goto err_rq;
> >
> >-              intel_engine_flush_submission(engine);
> >+              /* Wait until we ack the release_queue and start timeslicing
> >*/
> >+              do {
> >+                      intel_engine_flush_submission(engine);
> >+              } while (READ_ONCE(engine->execlists.pending[0]));
> 
> Is this guaranteed to clear?  Or should there be a count to protect against
> the endless loop?

Yes. If the HW stops, we reset it and clear the submission queue.
-Chris