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"
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;
