Re: [PATCH v2] drm/i915/gt: Hold a wakeref for the active VM

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On 31/03/2023 15:16, Andrzej Hajda wrote:
From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>

There may be a disconnect between the GT used by the engine and the GT
used for the VM, requiring us to hold a wakeref on both while the GPU is
active with this request.

v2: added explanation to __queue_and_release_pm

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
[ahajda: removed not-yet-upstremed wakeref tracking bits]
Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
---
Changes in v2:
- Link to v1: https://lore.kernel.org/r/20230330-hold_wakeref_for_active_vm-v1-1-baca712692f6@xxxxxxxxx
---
  drivers/gpu/drm/i915/gt/intel_context.h   | 15 +++++++++++----
  drivers/gpu/drm/i915/gt/intel_engine_pm.c |  9 +++++++++
  2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
index 0a8d553da3f439..48f888c3da083b 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.h
+++ b/drivers/gpu/drm/i915/gt/intel_context.h
@@ -14,6 +14,7 @@
  #include "i915_drv.h"
  #include "intel_context_types.h"
  #include "intel_engine_types.h"
+#include "intel_gt_pm.h"
  #include "intel_ring_types.h"
  #include "intel_timeline_types.h"
  #include "i915_trace.h"
@@ -207,8 +208,11 @@ void intel_context_exit_engine(struct intel_context *ce);
  static inline void intel_context_enter(struct intel_context *ce)
  {
  	lockdep_assert_held(&ce->timeline->mutex);
-	if (!ce->active_count++)
-		ce->ops->enter(ce);
+	if (ce->active_count++)
+		return;
+
+	ce->ops->enter(ce);
+	intel_gt_pm_get(ce->vm->gt);
  }
static inline void intel_context_mark_active(struct intel_context *ce)
@@ -222,8 +226,11 @@ static inline void intel_context_exit(struct intel_context *ce)
  {
  	lockdep_assert_held(&ce->timeline->mutex);
  	GEM_BUG_ON(!ce->active_count);
-	if (!--ce->active_count)
-		ce->ops->exit(ce);
+	if (--ce->active_count)
+		return;
+
+	intel_gt_pm_put_async(ce->vm->gt);
+	ce->ops->exit(ce);
  }
static inline struct intel_context *intel_context_get(struct intel_context *ce)
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
index e971b153fda976..ee531a5c142c77 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
@@ -114,6 +114,15 @@ __queue_and_release_pm(struct i915_request *rq,
ENGINE_TRACE(engine, "parking\n"); + /*
+	 * Open coded one half of intel_context_enter, which we have to omit
+	 * here (see the large comment below) and because the other part must
+	 * not be called due constructing directly with __i915_request_create
+	 * which increments active count via intel_context_mark_active.
+	 */
+	GEM_BUG_ON(rq->context->active_count != 1);
+	__intel_gt_pm_get(engine->gt);
+
  	/*
  	 * We have to serialise all potential retirement paths with our
  	 * submission, as we don't want to underflow either the

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko



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