[PATCH v2] drm/i915: Filter out spurious execlists context-switch interrupts

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Back in commit a4b2b01523a8 ("drm/i915: Don't mark an execlists
context-switch when idle") we noticed the presence of late
context-switch interrupts. We were able to filter those out by looking
at whether the ELSP remained active, but in commit beecec901790
("drm/i915/execlists: Preemption!") that became problematic as we now
anticipate receiving a context-switch event for preemption while ELSP
may be empty. To restore the spurious interrupt suppression, add a
counter for the expected number of pending context-switches and skip if
we do not need to handle this interrupt to make forward progress.

v2: Add the missing inc(active) for preempt.

Fixes: beecec901790 ("drm/i915/execlists: Preemption!")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Michal Winiarski <michal.winiarski@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Arkadiusz Hiler <arkadiusz.hiler@xxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_guc_submission.c | 11 ++++++-----
 drivers/gpu/drm/i915/i915_irq.c            |  6 ++++--
 drivers/gpu/drm/i915/intel_engine_cs.c     |  5 +++--
 drivers/gpu/drm/i915/intel_lrc.c           | 22 ++++++++++++++++++----
 drivers/gpu/drm/i915/intel_ringbuffer.h    |  7 +++++++
 5 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index a2e8114b739d..c22d0a07467c 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -550,11 +550,9 @@ static void port_assign(struct execlist_port *port,
 			struct drm_i915_gem_request *rq)
 {
 	GEM_BUG_ON(rq == port_request(port));
+	GEM_BUG_ON(port_isset(port));
 
-	if (port_isset(port))
-		i915_gem_request_put(port_request(port));
-
-	port_set(port, port_pack(i915_gem_request_get(rq), port_count(port)));
+	port_set(port, i915_gem_request_get(rq));
 	nested_enable_signaling(rq);
 }
 
@@ -586,8 +584,10 @@ static void i915_guc_dequeue(struct intel_engine_cs *engine)
 					goto done;
 				}
 
-				if (submit)
+				if (submit) {
 					port_assign(port, last);
+					execlists->active++;
+				}
 				port++;
 			}
 
@@ -610,6 +610,7 @@ static void i915_guc_dequeue(struct intel_engine_cs *engine)
 	execlists->first = rb;
 	if (submit) {
 		port_assign(port, last);
+		execlists->active++;
 		i915_guc_submit(engine);
 	}
 	spin_unlock_irq(&engine->timeline->lock);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b1296a55c1e4..f8205841868b 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1388,8 +1388,10 @@ gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift)
 	bool tasklet = false;
 
 	if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift)) {
-		__set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
-		tasklet = true;
+		if (READ_ONCE(engine->execlists.active)) {
+			__set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
+			tasklet = true;
+		}
 	}
 
 	if (iir & (GT_RENDER_USER_INTERRUPT << test_shift)) {
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index a47a9c6bea52..8aecbc321786 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1548,8 +1548,8 @@ bool intel_engine_is_idle(struct intel_engine_cs *engine)
 	if (test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted))
 		return false;
 
-	/* Both ports drained, no more ELSP submission? */
-	if (port_request(&engine->execlists.port[0]))
+	/* Waiting to drain ELSP? */
+	if (READ_ONCE(engine->execlists.active))
 		return false;
 
 	/* ELSP is empty, but there are ready requests? */
@@ -1749,6 +1749,7 @@ void intel_engine_dump(struct intel_engine_cs *engine, struct drm_printer *m)
 					   idx);
 			}
 		}
+		drm_printf(m, "\t\tELSP active %d\n", execlists->active);
 		rcu_read_unlock();
 	} else if (INTEL_GEN(dev_priv) > 6) {
 		drm_printf(m, "\tPP_DIR_BASE: 0x%08x\n",
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7f45dd7dc3e5..c2cdb85db365 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -482,15 +482,23 @@ static bool can_merge_ctx(const struct i915_gem_context *prev,
 	return true;
 }
 
-static void port_assign(struct execlist_port *port,
+static bool port_assign(struct execlist_port *port,
 			struct drm_i915_gem_request *rq)
 {
+	bool was_idle;
+
 	GEM_BUG_ON(rq == port_request(port));
 
-	if (port_isset(port))
+	if (port_isset(port)) {
 		i915_gem_request_put(port_request(port));
+		was_idle = false;
+	} else {
+		was_idle = true;
+	}
 
 	port_set(port, port_pack(i915_gem_request_get(rq), port_count(port)));
+
+	return was_idle;
 }
 
 static void inject_preempt_context(struct intel_engine_cs *engine)
@@ -576,6 +584,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 			 */
 			inject_preempt_context(engine);
 			execlists->preempt = true;
+			execlists->active++;
 			goto unlock;
 		} else {
 			/*
@@ -657,7 +666,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 				GEM_BUG_ON(last->ctx == rq->ctx);
 
 				if (submit)
-					port_assign(port, last);
+					execlists->active += port_assign(port, last);
 				port++;
 
 				GEM_BUG_ON(port_isset(port));
@@ -679,7 +688,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 done:
 	execlists->first = rb;
 	if (submit)
-		port_assign(port, last);
+		execlists->active += port_assign(port, last);
 unlock:
 	spin_unlock_irq(&engine->timeline->lock);
 
@@ -696,10 +705,12 @@ execlist_cancel_port_requests(struct intel_engine_execlists *execlists)
 	while (num_ports-- && port_isset(port)) {
 		struct drm_i915_gem_request *rq = port_request(port);
 
+		GEM_BUG_ON(!execlists->active);
 		execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_PREEMPTED);
 		i915_gem_request_put(rq);
 
 		memset(port, 0, sizeof(*port));
+		execlists->active--;
 		port++;
 	}
 }
@@ -863,6 +874,8 @@ static void intel_lrc_irq_handler(unsigned long data)
 
 				GEM_BUG_ON(!execlists->preempt);
 				execlists->preempt = false;
+				execlists->active--;
+				GEM_BUG_ON(execlists->active);
 				continue;
 			}
 
@@ -1461,6 +1474,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
 	clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
 	execlists->csb_head = -1;
 	execlists->preempt = false;
+	execlists->active = 0;
 
 	/* After a GPU reset, we may have requests to replay */
 	if (!i915_modparams.enable_guc_submission && execlists->first)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 17186f067408..588f5fe9d2b7 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -245,6 +245,11 @@ struct intel_engine_execlists {
 	 */
 	bool preempt;
 
+	/**
+	 * @active: count of the number of outstanding CSB events
+	 */
+	unsigned int active;
+
 	/**
 	 * @port_mask: number of execlist ports - 1
 	 */
@@ -538,9 +543,11 @@ execlists_port_complete(struct intel_engine_execlists * const execlists,
 	const unsigned int m = execlists->port_mask;
 
 	GEM_BUG_ON(port_index(port, execlists) != 0);
+	GEM_BUG_ON(!execlists->active);
 
 	memmove(port, port + 1, m * sizeof(struct execlist_port));
 	memset(port + m, 0, sizeof(struct execlist_port));
+	execlists->active--;
 }
 
 static inline unsigned int
-- 
2.15.0.rc1

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