5 files changed, 245 insertions, 12 deletions

diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
index 4eeba588b996..2d172991024f 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.c
+++ b/drivers/gpu/drm/i915/i915_scheduler.c
@@ -238,6 +238,18 @@ sched_lock_engine(struct i915_sched_node *node, struct intel_engine_cs *locked)
 	return engine;
 }
 
+static bool inflight(const struct i915_request *rq,
+		     const struct intel_engine_cs *engine)
+{
+	const struct i915_request *active;
+
+	if (!rq->global_seqno)
+		return false;
+
+	active = port_request(engine->execlists.port);
+	return active->hw_context == rq->hw_context;
+}
+
 static void __i915_schedule(struct i915_request *rq,
 			    const struct i915_sched_attr *attr)
 {
@@ -327,6 +339,7 @@ static void __i915_schedule(struct i915_request *rq,
 		INIT_LIST_HEAD(&dep->dfs_link);
 
 		engine = sched_lock_engine(node, engine);
+		lockdep_assert_held(&engine->timeline.lock);
 
 		/* Recheck after acquiring the engine->timeline.lock */
 		if (prio <= node->attr.priority || node_signaled(node))
@@ -355,17 +368,16 @@ static void __i915_schedule(struct i915_request *rq,
 		if (prio <= engine->execlists.queue_priority_hint)
 			continue;
 
+		engine->execlists.queue_priority_hint = prio;
+
 		/*
 		 * If we are already the currently executing context, don't
 		 * bother evaluating if we should preempt ourselves.
 		 */
-		if (node_to_request(node)->global_seqno &&
-		    i915_seqno_passed(port_request(engine->execlists.port)->global_seqno,
-				      node_to_request(node)->global_seqno))
+		if (inflight(node_to_request(node), engine))
 			continue;
 
 		/* Defer (tasklet) submission until after all of our updates. */
-		engine->execlists.queue_priority_hint = prio;
 		tasklet_hi_schedule(&engine->execlists.tasklet);
 	}
 
diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
index f12ecc8dec6b..8bc8aa54aa35 100644
--- a/drivers/gpu/drm/i915/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/intel_guc_submission.c
@@ -629,6 +629,8 @@ static void inject_preempt_context(struct work_struct *work)
 				       EXECLISTS_ACTIVE_PREEMPT);
 		tasklet_schedule(&engine->execlists.tasklet);
 	}
+
+	(void)I915_SELFTEST_ONLY(engine->execlists.preempt_hang.count++);
 }
 
 /*
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index a1034f7069aa..a9eb0211ce77 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -188,13 +188,90 @@ static inline int rq_prio(const struct i915_request *rq)
 	return rq->sched.attr.priority;
 }
 
+static int queue_prio(const struct intel_engine_execlists *execlists)
+{
+	struct i915_priolist *p;
+	struct rb_node *rb;
+
+	rb = rb_first_cached(&execlists->queue);
+	if (!rb)
+		return INT_MIN;
+
+	/*
+	 * As the priolist[] are inverted, with the highest priority in [0],
+	 * we have to flip the index value to become priority.
+	 */
+	p = to_priolist(rb);
+	return ((p->priority + 1) << I915_USER_PRIORITY_SHIFT) - ffs(p->used);
+}
+
 static inline bool need_preempt(const struct intel_engine_cs *engine,
-				const struct i915_request *last,
-				int prio)
+				const struct i915_request *rq)
+{
+	const int last_prio = rq_prio(rq);
+
+	if (!intel_engine_has_preemption(engine))
+		return false;
+
+	if (i915_request_completed(rq))
+		return false;
+
+	/*
+	 * Check if the current priority hint merits a preemption attempt.
+	 *
+	 * We record the highest value priority we saw during rescheduling
+	 * prior to this dequeue, therefore we know that if it is strictly
+	 * less than the current tail of ESLP[0], we do not need to force
+	 * a preempt-to-idle cycle.
+	 *
+	 * However, the priority hint is a mere hint that we may need to
+	 * preempt. If that hint is stale or we may be trying to preempt
+	 * ourselves, ignore the request.
+	 */
+	if (!__execlists_need_preempt(engine->execlists.queue_priority_hint,
+				      last_prio))
+		return false;
+
+	/*
+	 * Check against the first request in ELSP[1], it will, thanks to the
+	 * power of PI, be the highest priority of that context.
+	 */
+	if (!list_is_last(&rq->link, &engine->timeline.requests) &&
+	    rq_prio(list_next_entry(rq, link)) > last_prio)
+		return true;
+
+	/*
+	 * If the inflight context did not trigger the preemption, then maybe
+	 * it was the set of queued requests? Pick the highest priority in
+	 * the queue (the first active priolist) and see if it deserves to be
+	 * running instead of ELSP[0].
+	 *
+	 * The highest priority request in the queue can not be either
+	 * ELSP[0] or ELSP[1] as, thanks again to PI, if it was the same
+	 * context, it's priority would not exceed ELSP[0] aka last_prio.
+	 */
+	return queue_prio(&engine->execlists) > last_prio;
+}
+
+__maybe_unused static inline bool
+assert_priority_queue(const struct intel_engine_execlists *execlists,
+		      const struct i915_request *prev,
+		      const struct i915_request *next)
 {
-	return (intel_engine_has_preemption(engine) &&
-		__execlists_need_preempt(prio, rq_prio(last)) &&
-		!i915_request_completed(last));
+	if (!prev)
+		return true;
+
+	/*
+	 * Without preemption, the prev may refer to the still active element
+	 * which we refuse to let go.
+	 *
+	 * Even with preemption, there are times when we think it is better not
+	 * to preempt and leave an ostensibly lower priority request in flight.
+	 */
+	if (port_request(execlists->port) == prev)
+		return true;
+
+	return rq_prio(prev) >= rq_prio(next);
 }
 
 /*
@@ -523,6 +600,8 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
 
 	execlists_clear_active(execlists, EXECLISTS_ACTIVE_HWACK);
 	execlists_set_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
+
+	(void)I915_SELFTEST_ONLY(execlists->preempt_hang.count++);
 }
 
 static void complete_preempt_context(struct intel_engine_execlists *execlists)
@@ -591,7 +670,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		if (!execlists_is_active(execlists, EXECLISTS_ACTIVE_HWACK))
 			return;
 
-		if (need_preempt(engine, last, execlists->queue_priority_hint)) {
+		if (need_preempt(engine, last)) {
 			inject_preempt_context(engine);
 			return;
 		}
@@ -637,8 +716,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		int i;
 
 		priolist_for_each_request_consume(rq, rn, p, i) {
-			GEM_BUG_ON(last &&
-				   need_preempt(engine, last, rq_prio(rq)));
+			GEM_BUG_ON(!assert_priority_queue(execlists, last, rq));
 
 			/*
 			 * Can we combine this request with the current port?
@@ -884,6 +962,8 @@ static void process_csb(struct intel_engine_cs *engine)
 	const u32 * const buf = execlists->csb_status;
 	u8 head, tail;
 
+	lockdep_assert_held(&engine->timeline.lock);
+
 	/*
 	 * Note that csb_write, csb_status may be either in HWSP or mmio.
 	 * When reading from the csb_write mmio register, we have to be
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index ef024c154a1b..953ccc2617ff 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -203,6 +203,7 @@ struct i915_priolist {
 
 struct st_preempt_hang {
 	struct completion completion;
+	unsigned int count;
 	bool inject_hang;
 };
 
diff --git a/drivers/gpu/drm/i915/selftests/intel_lrc.c b/drivers/gpu/drm/i915/selftests/intel_lrc.c
index 2b2ecd76c2ac..fb35f53c9ce3 100644
--- a/drivers/gpu/drm/i915/selftests/intel_lrc.c
+++ b/drivers/gpu/drm/i915/selftests/intel_lrc.c
@@ -268,6 +268,143 @@ err_wedged:
 	goto err_ctx_lo;
 }
 
+struct preempt_client {
+	struct igt_spinner spin;
+	struct i915_gem_context *ctx;
+};
+
+static int preempt_client_init(struct drm_i915_private *i915,
+			       struct preempt_client *c)
+{
+	c->ctx = kernel_context(i915);
+	if (!c->ctx)
+		return -ENOMEM;
+
+	if (igt_spinner_init(&c->spin, i915))
+		goto err_ctx;
+
+	return 0;
+
+err_ctx:
+	kernel_context_close(c->ctx);
+	return -ENOMEM;
+}
+
+static void preempt_client_fini(struct preempt_client *c)
+{
+	igt_spinner_fini(&c->spin);
+	kernel_context_close(c->ctx);
+}
+
+static int live_suppress_self_preempt(void *arg)
+{
+	struct drm_i915_private *i915 = arg;
+	struct intel_engine_cs *engine;
+	struct i915_sched_attr attr = {
+		.priority = I915_USER_PRIORITY(I915_PRIORITY_MAX)
+	};
+	struct preempt_client a, b;
+	enum intel_engine_id id;
+	intel_wakeref_t wakeref;
+	int err = -ENOMEM;
+
+	/*
+	 * Verify that if a preemption request does not cause a change in
+	 * the current execution order, the preempt-to-idle injection is
+	 * skipped and that we do not accidentally apply it after the CS
+	 * completion event.
+	 */
+
+	if (!HAS_LOGICAL_RING_PREEMPTION(i915))
+		return 0;
+
+	if (USES_GUC_SUBMISSION(i915))
+		return 0; /* presume black blox */
+
+	mutex_lock(&i915->drm.struct_mutex);
+	wakeref = intel_runtime_pm_get(i915);
+
+	if (preempt_client_init(i915, &a))
+		goto err_unlock;
+	if (preempt_client_init(i915, &b))
+		goto err_client_a;
+
+	for_each_engine(engine, i915, id) {
+		struct i915_request *rq_a, *rq_b;
+		int depth;
+
+		engine->execlists.preempt_hang.count = 0;
+
+		rq_a = igt_spinner_create_request(&a.spin,
+						  a.ctx, engine,
+						  MI_NOOP);
+		if (IS_ERR(rq_a)) {
+			err = PTR_ERR(rq_a);
+			goto err_client_b;
+		}
+
+		i915_request_add(rq_a);
+		if (!igt_wait_for_spinner(&a.spin, rq_a)) {
+			pr_err("First client failed to start\n");
+			goto err_wedged;
+		}
+
+		for (depth = 0; depth < 8; depth++) {
+			rq_b = igt_spinner_create_request(&b.spin,
+							  b.ctx, engine,
+							  MI_NOOP);
+			if (IS_ERR(rq_b)) {
+				err = PTR_ERR(rq_b);
+				goto err_client_b;
+			}
+			i915_request_add(rq_b);
+
+			GEM_BUG_ON(i915_request_completed(rq_a));
+			engine->schedule(rq_a, &attr);
+			igt_spinner_end(&a.spin);
+
+			if (!igt_wait_for_spinner(&b.spin, rq_b)) {
+				pr_err("Second client failed to start\n");
+				goto err_wedged;
+			}
+
+			swap(a, b);
+			rq_a = rq_b;
+		}
+		igt_spinner_end(&a.spin);
+
+		if (engine->execlists.preempt_hang.count) {
+			pr_err("Preemption recorded x%d, depth %d; should have been suppressed!\n",
+			       engine->execlists.preempt_hang.count,
+			       depth);
+			err = -EINVAL;
+			goto err_client_b;
+		}
+
+		if (igt_flush_test(i915, I915_WAIT_LOCKED))
+			goto err_wedged;
+	}
+
+	err = 0;
+err_client_b:
+	preempt_client_fini(&b);
+err_client_a:
+	preempt_client_fini(&a);
+err_unlock:
+	if (igt_flush_test(i915, I915_WAIT_LOCKED))
+		err = -EIO;
+	intel_runtime_pm_put(i915, wakeref);
+	mutex_unlock(&i915->drm.struct_mutex);
+	return err;
+
+err_wedged:
+	igt_spinner_end(&b.spin);
+	igt_spinner_end(&a.spin);
+	i915_gem_set_wedged(i915);
+	err = -EIO;
+	goto err_client_b;
+}
+
 static int live_preempt_hang(void *arg)
 {
 	struct drm_i915_private *i915 = arg;
@@ -647,6 +784,7 @@ int intel_execlists_live_selftests(struct drm_i915_private *i915)
 		SUBTEST(live_sanitycheck),
 		SUBTEST(live_preempt),
 		SUBTEST(live_late_preempt),
+		SUBTEST(live_suppress_self_preempt),
 		SUBTEST(live_preempt_hang),
 		SUBTEST(live_preempt_smoke),
 	};