[PATCH 4/6] drm/i915: Harden detection of missed interrupts

[Chris Wilson <chris@chris-wilson.co.uk>]

Only declare a missed interrupt if we find that the GPU is idle with
waiters and a hangcheck interval has passed in which no new user
interrupts have been raised.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c     | 11 +++++++----
 drivers/gpu/drm/i915/i915_irq.c         |  7 ++++++-
 drivers/gpu/drm/i915/intel_ringbuffer.h |  2 ++
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index b421b53ca128..966fc022418c 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -730,10 +730,10 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
 static void i915_ring_seqno_info(struct seq_file *m,
 				 struct intel_engine_cs *ring)
 {
-	if (ring->get_seqno) {
-		seq_printf(m, "Current sequence (%s): %x\n",
-			   ring->name, ring->get_seqno(ring));
-	}
+	seq_printf(m, "Current sequence (%s): %x\n",
+		   ring->name, ring->get_seqno(ring));
+	seq_printf(m, "Current user interrupts (%s): %x\n",
+		   ring->name, READ_ONCE(ring->user_interrupts));
 }
 
 static int i915_gem_seqno_info(struct seq_file *m, void *data)
@@ -1361,6 +1361,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 		seq_printf(m, "%s:\n", ring->name);
 		seq_printf(m, "\tseqno = %x [current %x]\n",
 			   ring->hangcheck.seqno, seqno[i]);
+		seq_printf(m, "\tuser interrupts = %x [current %x]\n",
+			   ring->hangcheck.user_interrupts,
+			   ring->user_interrupts);
 		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
 			   (long long)ring->hangcheck.acthd,
 			   (long long)acthd[i]);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 07bc2cdd6252..978eebcf4594 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1000,6 +1000,7 @@ static void notify_ring(struct intel_engine_cs *ring)
 		return;
 
 	trace_i915_gem_request_notify(ring);
+	ring->user_interrupts++;
 
 	wake_up_all(&ring->irq_queue);
 }
@@ -3097,6 +3098,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 	for_each_ring(ring, dev_priv, i) {
 		u64 acthd;
 		u32 seqno;
+		unsigned user_interrupts;
 		bool busy = true;
 
 		semaphore_clear_deadlocks(dev_priv);
@@ -3113,6 +3115,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 
 		acthd = intel_ring_get_active_head(ring);
 		seqno = ring->get_seqno(ring);
+		user_interrupts = READ_ONCE(ring->user_interrupts);
 
 		if (ring->hangcheck.seqno == seqno) {
 			if (ring_idle(ring, seqno)) {
@@ -3120,7 +3123,8 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 
 				if (waitqueue_active(&ring->irq_queue)) {
 					/* Issue a wake-up to catch stuck h/w. */
-					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
+					if (ring->hangcheck.user_interrupts == user_interrupts &&
+					    !test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
 						if (!(dev_priv->gpu_error.test_irq_rings & intel_ring_flag(ring)))
 							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
 								  ring->name);
@@ -3187,6 +3191,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 
 		ring->hangcheck.seqno = seqno;
 		ring->hangcheck.acthd = acthd;
+		ring->hangcheck.user_interrupts = user_interrupts;
 		busy_count += busy;
 	}
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 8fb02b21e75d..b22573561669 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -90,6 +90,7 @@ struct intel_ring_hangcheck {
 	u64 acthd;
 	u64 max_acthd;
 	u32 seqno;
+	unsigned user_interrupts;
 	int score;
 	enum intel_ring_hangcheck_action action;
 	int deadlock;
@@ -301,6 +302,7 @@ struct  intel_engine_cs {
 	 * inspecting request list.
 	 */
 	u32 last_submitted_seqno;
+	unsigned user_interrupts;
 
 	bool gpu_caches_dirty;
 
-- 
2.7.0.rc3

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