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@intel.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
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;