Re: [Intel-gfx] [PATCH 04/26] drm/i915/guc: Don't call switch_to_kernel_context with GuC submission

John Harrison
2021-10-07T03:49:14Z

On 10/4/2021 15:06, Matthew Brost wrote:
> Calling switch_to_kernel_context isn't needed if the engine PM reference
> is taken while all user contexts are pinned as if don't have PM ref that
> guarantees that all user contexts scheduling is disabled. By not calling
> switch_to_kernel_context we save on issuing a request to the engine.
>
> v2:
> (Daniel Vetter)
> - Add FIXME comment about pushing switch_to_kernel_context to backend
> v3:
> (John Harrison)
> - Update commit message
> - Fix workding comment
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>

> ---
> drivers/gpu/drm/i915/gt/intel_engine_pm.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> index dacd62773735..a1334b48dde7 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> @@ -162,6 +162,19 @@ static bool switch_to_kernel_context(struct intel_engine_cs *engine)
> unsigned long flags;
> bool result = true;
>
> + /*
> + * This is execlist specific behaviour intended to ensure the GPU is
> + * idle by switching to a known 'safe' context. With GuC submission, the
> + * same idle guarantee is achieved by other means (disabling
> + * scheduling). Further, switching to a 'safe' context has no effect
> + * with GuC submission as the scheduler can just switch back again.
> + *
> + * FIXME: Move this backend scheduler specific behaviour into the
> + * scheduler 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;