[PATCH 16/19] drm/i915/execlists: Try preempt-reset from softirq context

[Chris Wilson]

When circumstances allow, trying resetting the engine directly from the
preemption timeout handler. As this is softirq context, we have to be
careful both not to sleep and not to spin on anything we may be
interrupting (e.g. the submission tasklet).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
CC: Michel Thierry <michel.thierry at intel.com>
Cc: Jeff McGee <jeff.mcgee at intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c           | 31 +++++++++-
 drivers/gpu/drm/i915/selftests/intel_lrc.c | 94 ++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 0e6e1b0bd966..7836a927425e 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -548,6 +548,33 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
 	execlists_set_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
 }
 
+static int try_preempt_reset(struct intel_engine_execlists *execlists)
+{
+	struct intel_engine_cs *engine =
+		container_of(execlists, typeof(*engine), execlists);
+	int err = -EBUSY;
+
+	if (!test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted) &&
+	    tasklet_trylock(&execlists->tasklet)) {
+		unsigned long *lock = &engine->i915->gpu_error.flags;
+		unsigned int bit = I915_RESET_ENGINE + engine->id;
+
+		if (!test_and_set_bit(bit, lock)) {
+			tasklet_disable_nosync(&engine->execlists.tasklet);
+			err = i915_reset_engine(engine,
+						"preemption time out");
+			tasklet_enable(&engine->execlists.tasklet);
+
+			clear_bit(bit, lock);
+			wake_up_bit(lock, bit);
+		}
+
+		tasklet_unlock(&execlists->tasklet);
+	}
+
+	return err;
+}
+
 static enum hrtimer_restart preempt_timeout(struct hrtimer *hrtimer)
 {
 	struct intel_engine_execlists *execlists =
@@ -561,7 +588,9 @@ static enum hrtimer_restart preempt_timeout(struct hrtimer *hrtimer)
 	if (!execlists_is_active(execlists, EXECLISTS_ACTIVE_PREEMPT_TIMEOUT))
 		return HRTIMER_NORESTART;
 
-	queue_work(system_highpri_wq, &execlists->preempt_reset);
+	if (try_preempt_reset(execlists))
+		queue_work(system_highpri_wq, &execlists->preempt_reset);
+
 	return HRTIMER_NORESTART;
 }
 
diff --git a/drivers/gpu/drm/i915/selftests/intel_lrc.c b/drivers/gpu/drm/i915/selftests/intel_lrc.c
index af16b0a40653..8d9efbd1b1e8 100644
--- a/drivers/gpu/drm/i915/selftests/intel_lrc.c
+++ b/drivers/gpu/drm/i915/selftests/intel_lrc.c
@@ -546,6 +546,99 @@ static int live_preempt_timeout(void *arg)
 	return err;
 }
 
+static int live_preempt_reset(void *arg)
+{
+	struct drm_i915_private *i915 = arg;
+	struct intel_engine_cs *engine;
+	struct i915_gem_context *ctx;
+	enum intel_engine_id id;
+	struct spinner spin;
+	int err = -ENOMEM;
+
+	if (!HAS_LOGICAL_RING_PREEMPTION(i915))
+		return 0;
+
+	mutex_lock(&i915->drm.struct_mutex);
+
+	if (spinner_init(&spin, i915))
+		goto err_unlock;
+
+	ctx= kernel_context(i915);
+	if (!ctx)
+		goto err_spin;
+
+	for_each_engine(engine, i915, id) {
+		struct i915_request *rq;
+
+		rq = spinner_create_request(&spin, ctx, engine, MI_NOOP);
+		if (IS_ERR(rq)) {
+			err = PTR_ERR(rq);
+			goto err_ctx;
+		}
+
+		i915_request_add(rq);
+		if (!wait_for_spinner(&spin, rq)) {
+			i915_gem_set_wedged(i915);
+			err = -EIO;
+			goto err_ctx;
+		}
+
+		/* Flush to improve our odds of enabling try_preempt_reset. */
+		do {
+			tasklet_schedule(&engine->execlists.tasklet);
+			tasklet_kill(&engine->execlists.tasklet);
+		} while (test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted));
+		GEM_BUG_ON(i915_request_completed(rq));
+
+		local_bh_disable(); /* emulate the timer/softirq context */
+		err = try_preempt_reset(&engine->execlists);
+		local_bh_enable();
+		if (err) {
+			pr_err("Preempt softirq reset failed on %s, irq_posted? %d, tasklet state %lx\n",
+			       engine->name,
+			       test_bit(ENGINE_IRQ_EXECLIST,
+					&engine->irq_posted),
+			       engine->execlists.tasklet.state);
+			i915_gem_set_wedged(i915);
+			goto err_ctx;
+		}
+
+		local_irq_disable(); /* emulate the timer/hardirq context */
+		err = try_preempt_reset(&engine->execlists);
+		local_irq_enable();
+		if (err) {
+			pr_err("Preempt hardirq reset failed on %s, irq_posted? %d, tasklet state %lx\n",
+			       engine->name,
+			       test_bit(ENGINE_IRQ_EXECLIST,
+					&engine->irq_posted),
+			       engine->execlists.tasklet.state);
+			i915_gem_set_wedged(i915);
+			goto err_ctx;
+		}
+
+		/*
+		 * In such a simple case as above; triggering a reset allows
+		 * us to save and restore the hog perfectly...
+		 */
+		spinner_end(&spin);
+
+		if (flush_test(i915, I915_WAIT_LOCKED)) {
+			err = -EIO;
+			goto err_ctx;
+		}
+	}
+
+	err = 0;
+err_ctx:
+	kernel_context_close(ctx);
+err_spin:
+	spinner_fini(&spin);
+err_unlock:
+	flush_test(i915, I915_WAIT_LOCKED);
+	mutex_unlock(&i915->drm.struct_mutex);
+	return err;
+}
+
 int intel_execlists_live_selftests(struct drm_i915_private *i915)
 {
 	static const struct i915_subtest tests[] = {
@@ -553,6 +646,7 @@ int intel_execlists_live_selftests(struct drm_i915_private *i915)
 		SUBTEST(live_preempt),
 		SUBTEST(live_late_preempt),
 		SUBTEST(live_preempt_timeout),
+		SUBTEST(live_preempt_reset),
 	};
 	return i915_subtests(tests, i915);
 }
-- 
2.16.3