Re: [PATCH 22/27] drm/i915/guc: Drop pin count check trick between sched_disable and re-pin

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On 8/18/2021 11:16 PM, Matthew Brost wrote:
Drop pin count check trick between a sched_disable and re-pin, now rely
on the lock and counter of the number of committed requests to determine
if scheduling should be disabled on the context.

Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>

Daniele

---
  drivers/gpu/drm/i915/gt/intel_context_types.h |  2 +
  .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 49 ++++++++++++-------
  2 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
index d5d643b04d54..524a35a78bf4 100644
--- a/drivers/gpu/drm/i915/gt/intel_context_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
@@ -169,6 +169,8 @@ struct intel_context {
  		struct list_head fences;
  		/* GuC context blocked fence */
  		struct i915_sw_fence blocked_fence;
+		/* GuC committed requests */
+		int number_committed_requests;
  	} guc_state;
struct {
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 5f77f25322ca..3e90985b0c1b 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -248,6 +248,25 @@ static inline void decr_context_blocked(struct intel_context *ce)
  	ce->guc_state.sched_state -= SCHED_STATE_BLOCKED;
  }
+static inline bool context_has_committed_requests(struct intel_context *ce)
+{
+	return !!ce->guc_state.number_committed_requests;
+}
+
+static inline void incr_context_committed_requests(struct intel_context *ce)
+{
+	lockdep_assert_held(&ce->guc_state.lock);
+	++ce->guc_state.number_committed_requests;
+	GEM_BUG_ON(ce->guc_state.number_committed_requests < 0);
+}
+
+static inline void decr_context_committed_requests(struct intel_context *ce)
+{
+	lockdep_assert_held(&ce->guc_state.lock);
+	--ce->guc_state.number_committed_requests;
+	GEM_BUG_ON(ce->guc_state.number_committed_requests < 0);
+}
+
  static inline bool context_guc_id_invalid(struct intel_context *ce)
  {
  	return ce->guc_id == GUC_INVALID_LRC_ID;
@@ -1751,14 +1770,11 @@ static void guc_context_sched_disable(struct intel_context *ce)
  	spin_lock_irqsave(&ce->guc_state.lock, flags);
/*
-	 * We have to check if the context has been disabled by another thread.
-	 * We also have to check if the context has been pinned again as another
-	 * pin operation is allowed to pass this function. Checking the pin
-	 * count, within ce->guc_state.lock, synchronizes this function with
-	 * guc_request_alloc ensuring a request doesn't slip through the
-	 * 'context_pending_disable' fence. Checking within the spin lock (can't
-	 * sleep) ensures another process doesn't pin this context and generate
-	 * a request before we set the 'context_pending_disable' flag here.
+	 * We have to check if the context has been disabled by another thread,
+	 * check if submssion has been disabled to seal a race with reset and
+	 * finally check if any more requests have been committed to the
+	 * context ensursing that a request doesn't slip through the
+	 * 'context_pending_disable' fence.
  	 */
  	enabled = context_enabled(ce);
  	if (unlikely(!enabled || submission_disabled(guc))) {
@@ -1767,7 +1783,8 @@ static void guc_context_sched_disable(struct intel_context *ce)
  		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
  		goto unpin;
  	}
-	if (unlikely(atomic_add_unless(&ce->pin_count, -2, 2))) {
+	if (unlikely(context_has_committed_requests(ce))) {
+		intel_context_sched_disable_unpin(ce);
  		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
  		return;
  	}
@@ -1800,6 +1817,7 @@ static void __guc_context_destroy(struct intel_context *ce)
  		   ce->guc_prio_count[GUC_CLIENT_PRIORITY_HIGH] ||
  		   ce->guc_prio_count[GUC_CLIENT_PRIORITY_KMD_NORMAL] ||
  		   ce->guc_prio_count[GUC_CLIENT_PRIORITY_NORMAL]);
+	GEM_BUG_ON(ce->guc_state.number_committed_requests);
lrc_fini(ce);
  	intel_context_fini(ce);
@@ -2030,6 +2048,10 @@ static void remove_from_context(struct i915_request *rq)
spin_unlock_irq(&ce->guc_active.lock); + spin_lock_irq(&ce->guc_state.lock);
+	decr_context_committed_requests(ce);
+	spin_unlock_irq(&ce->guc_state.lock);
+
  	atomic_dec(&ce->guc_id_ref);
  	i915_request_notify_execute_cb_imm(rq);
  }
@@ -2177,15 +2199,7 @@ static int guc_request_alloc(struct i915_request *rq)
  	 * schedule enable or context registration if either G2H is pending
  	 * respectfully. Once a G2H returns, the fence is released that is
  	 * blocking these requests (see guc_signal_context_fence).
-	 *
-	 * We can safely check the below fields outside of the lock as it isn't
-	 * possible for these fields to transition from being clear to set but
-	 * converse is possible, hence the need for the check within the lock.
  	 */
-	if (likely(!context_wait_for_deregister_to_register(ce) &&
-		   !context_pending_disable(ce)))
-		return 0;
-
  	spin_lock_irqsave(&ce->guc_state.lock, flags);
  	if (context_wait_for_deregister_to_register(ce) ||
  	    context_pending_disable(ce)) {
@@ -2194,6 +2208,7 @@ static int guc_request_alloc(struct i915_request *rq)
list_add_tail(&rq->guc_fence_link, &ce->guc_state.fences);
  	}
+	incr_context_committed_requests(ce);
  	spin_unlock_irqrestore(&ce->guc_state.lock, flags);
return 0;




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