On Thu, Sep 09, 2021 at 03:51:27PM -0700, John Harrison wrote: > On 8/20/2021 15:44, Matthew Brost wrote: > > Calling switch_to_kernel_context isn't needed if the engine PM reference > > is taken while all contexts are pinned. By not calling > > switch_to_kernel_context we save on issuing a request to the engine. > I thought the intention of the switch_to_kernel was to ensure that the GPU > is not touching any user context and is basically idle. That is not a valid > assumption with an external scheduler such as GuC. So why is the description > above only mentioning PM references? What is the connection between the PM > ref and the switch_to_kernel? > > Also, the comment in the code does not mention anything about PM references, > it just says 'not necessary with GuC' but no explanation at all. > > > > v2: > > (Daniel Vetter) > > - Add FIXME comment about pushing switch_to_kernel_context to backend > > > > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx> > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > > --- > > drivers/gpu/drm/i915/gt/intel_engine_pm.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c > > index 1f07ac4e0672..11fee66daf60 100644 > > --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c > > +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c > > @@ -162,6 +162,15 @@ static bool switch_to_kernel_context(struct intel_engine_cs *engine) > > unsigned long flags; > > bool result = true; > > + /* > > + * No need to switch_to_kernel_context if GuC submission > > + * > > + * FIXME: This execlists specific backend behavior in generic code, this > "This execlists" -> "This is execlist" > > "this should be" -> "it should be" > Missed this. Will fix in next rev. Matt > John. > > > + * should be pushed to the backend. > > + */ > > + if (intel_engine_uses_guc(engine)) > > + return true; > > + > > /* GPU is pointing to the void, as good as in the kernel context. */ > > if (intel_gt_is_wedged(engine->gt)) > > return true; >
