[Intel-gfx] [RFC PATCH 53/97] drm/i915/guc: Disable semaphores when using GuC scheduling

[Matthew Brost]

On Wed, May 26, 2021 at 10:25:13AM +0100, Tvrtko Ursulin wrote:
> 
> On 25/05/2021 18:01, Matthew Brost wrote:
> > On Tue, May 25, 2021 at 10:52:01AM +0100, Tvrtko Ursulin wrote:
> > > 
> > > On 06/05/2021 20:14, Matthew Brost wrote:
> > > > Disable semaphores when using GuC scheduling as semaphores are broken in
> > > > the current GuC firmware.
> > > 
> > > What is "current"? Given that the patch itself is like year and a half old.
> > > 
> > 
> > Stale comment. Semaphore work with the firmware we just haven't enabled
> > them in the i915 with GuC submission as this an optimization and not
> > required for functionality.
> 
> How will the updated commit message look in terms of remaining reasons why
> semaphores won't/can't be enabled?
> 

Semaphores are an optimization and not required for basic GuC submission
to work properly. Disable until we have time to do the implementation to
enable semaphores and tune them for performance.

> They were a nice performance win on some media workloads although granted a
> lot of tweaking was required to find a good balance on when to use them and
> when not to.
>

The same tweaking would have to be done for with GuC submission. Let's
get basic submission then tweak for performance.

Matt 
 
> Regards,
> 
> Tvrtko
> 
> > Matt
> > 
> > > Regards,
> > > 
> > > Tvrtko
> > > 
> > > > Cc: John Harrison <john.c.harrison at intel.com>
> > > > Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> > > > ---
> > > >    drivers/gpu/drm/i915/gem/i915_gem_context.c | 6 ++++--
> > > >    1 file changed, 4 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > > > index 993faa213b41..d30260ffe2a7 100644
> > > > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > > > @@ -230,7 +230,8 @@ static void intel_context_set_gem(struct intel_context *ce,
> > > >    		ce->timeline = intel_timeline_get(ctx->timeline);
> > > >    	if (ctx->sched.priority >= I915_PRIORITY_NORMAL &&
> > > > -	    intel_engine_has_timeslices(ce->engine))
> > > > +	    intel_engine_has_timeslices(ce->engine) &&
> > > > +	    intel_engine_has_semaphores(ce->engine))
> > > >    		__set_bit(CONTEXT_USE_SEMAPHORES, &ce->flags);
> > > >    	intel_context_set_watchdog_us(ce, ctx->watchdog.timeout_us);
> > > > @@ -1939,7 +1940,8 @@ static int __apply_priority(struct intel_context *ce, void *arg)
> > > >    	if (!intel_engine_has_timeslices(ce->engine))
> > > >    		return 0;
> > > > -	if (ctx->sched.priority >= I915_PRIORITY_NORMAL)
> > > > +	if (ctx->sched.priority >= I915_PRIORITY_NORMAL &&
> > > > +	    intel_engine_has_semaphores(ce->engine))
> > > >    		intel_context_set_use_semaphores(ce);
> > > >    	else
> > > >    		intel_context_clear_use_semaphores(ce);
> > > >