[Intel-gfx] [PATCH 1/4] drm/i915/selftests: Split preemption smoke test into threads

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-10-01 11:38:37)
> 
> On 28/09/2018 14:58, Chris Wilson wrote:
> > When submitting chains to each engine, we can do so (mostly) in
> > parallel, so delegate submission to threads on a per-engine basis.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >   drivers/gpu/drm/i915/selftests/intel_lrc.c | 73 ++++++++++++++++++----
> >   1 file changed, 61 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/selftests/intel_lrc.c b/drivers/gpu/drm/i915/selftests/intel_lrc.c
> > index 3a474bb64c05..d68a924c530e 100644
> > --- a/drivers/gpu/drm/i915/selftests/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/selftests/intel_lrc.c
> > @@ -587,8 +587,10 @@ static int random_priority(struct rnd_state *rnd)
> >   struct preempt_smoke {
> >       struct drm_i915_private *i915;
> >       struct i915_gem_context **contexts;
> > +     struct intel_engine_cs *engine;
> >       unsigned int ncontext;
> >       struct rnd_state prng;
> > +     unsigned long count;
> >   };
> >   
> >   static struct i915_gem_context *smoke_context(struct preempt_smoke *smoke)
> > @@ -597,31 +599,78 @@ static struct i915_gem_context *smoke_context(struct preempt_smoke *smoke)
> >                                                         &smoke->prng)];
> >   }
> >   
> > +static int smoke_crescendo_thread(void *arg)
> > +{
> > +     struct preempt_smoke *smoke = arg;
> > +     IGT_TIMEOUT(end_time);
> > +     unsigned long count;
> > +
> > +     count = 0;
> > +     do {
> > +             struct i915_gem_context *ctx = smoke_context(smoke);
> > +             struct i915_request *rq;
> > +
> > +             mutex_lock(&smoke->i915->drm.struct_mutex);
> > +
> > +             ctx->sched.priority = count % I915_PRIORITY_MAX;
> > +
> > +             rq = i915_request_alloc(smoke->engine, ctx);
> > +             if (IS_ERR(rq)) {
> > +                     mutex_unlock(&smoke->i915->drm.struct_mutex);
> > +                     return PTR_ERR(rq);
> > +             }
> > +
> > +             i915_request_add(rq);
> > +
> > +             mutex_unlock(&smoke->i915->drm.struct_mutex);
> > +
> > +             count++;
> 
> Very little outside the mutex so I am not sure if parallelization will 
> work that well. Every thread could probably fill the ring in it's 
> timeslice?

Very unlikely due to the randomised ring. And we are working on that,
right? :)

> And then it blocks the others until there is space. It will 
> heavily rely on scheduler behaviour and mutex fairness I think.

But it does bring the overall subtest time from num_engines to 1s, for
the same pattern.
-Chris