drm/i915: Retire requests along rings

In the next patch, rings are the central timeline as requests may jump
between engines. Therefore in the future as we retire in order along the
engine timeline, we may retire out-of-order within a ring (as the ring now
occurs along multiple engines), leading to much hilarity in miscomputing
the position of ring->head.

As an added bonus, retiring along the ring reduces the penalty of having
one execlists client do cleanup for another (old legacy submission
shares a ring between all clients). The downside is that slow and
irregular (off the critical path) process of cleaning up stale requests
after userspace becomes a modicum less efficient.

In the long run, it will become apparent that the ordered
ring->request_list matches the ring->timeline, a fun challenge for the
future will be unifying the two lists to avoid duplication!

v2: We need both engine-order and ring-order processing to maintain our
knowledge of where individual rings have completed upto as well as
knowing what was last executing on any engine. And finally by decoupling
retiring the contexts on the engine and the timelines along the rings,
we do have to keep a reference to the context on each request
(previously it was guaranteed by the context being pinned).

v3: Not just a reference to the context, but we need to keep it pinned
as we manipulate the rings; i.e. we need a pin for both the manipulation
of the engine state during its retirements, and a separate pin for the
manipulation of the ring state.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
Reviewed-by: Tvrtko Ursulin <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: ickle

drivers/gpu/drm/i915/i915_drv.h

@@ -2059,8 +2059,9 @@ struct drm_i915_private {
 		void (*resume)(struct drm_i915_private *);
 		void (*cleanup_engine)(struct intel_engine_cs *engine);
 
-		struct list_head timelines;
 		struct i915_gem_timeline global_timeline;
+		struct list_head timelines;
+		struct list_head rings;
 		u32 active_requests;
 		u32 request_serial;
 

drivers/gpu/drm/i915/i915_gem.c

@@ -5600,6 +5600,7 @@ int i915_gem_init_early(struct drm_i915_private *dev_priv)
 		goto err_dependencies;
 
 	mutex_lock(&dev_priv->drm.struct_mutex);
+	INIT_LIST_HEAD(&dev_priv->gt.rings);
 	INIT_LIST_HEAD(&dev_priv->gt.timelines);
 	err = i915_gem_timeline_init__global(dev_priv);
 	mutex_unlock(&dev_priv->drm.struct_mutex);

drivers/gpu/drm/i915/i915_request.c

@@ -286,6 +286,7 @@ static int reserve_gt(struct drm_i915_private *i915)
 
 static void unreserve_gt(struct drm_i915_private *i915)
 {
+	GEM_BUG_ON(!i915->gt.active_requests);
 	if (!--i915->gt.active_requests)
 		i915_gem_park(i915);
 }
@@ -298,6 +299,7 @@ void i915_gem_retire_noop(struct i915_gem_active *active,
 
 static void advance_ring(struct i915_request *request)
 {
+	struct intel_ring *ring = request->ring;
 	unsigned int tail;
 
 	/*
@@ -309,7 +311,8 @@ static void advance_ring(struct i915_request *request)
 	 * Note this requires that we are always called in request
 	 * completion order.
 	 */
-	if (list_is_last(&request->ring_link, &request->ring->request_list)) {
+	GEM_BUG_ON(!list_is_first(&request->ring_link, &ring->request_list));
+	if (list_is_last(&request->ring_link, &ring->request_list)) {
 		/*
 		 * We may race here with execlists resubmitting this request
 		 * as we retire it. The resubmission will move the ring->tail
@@ -322,9 +325,9 @@ static void advance_ring(struct i915_request *request)
 	} else {
 		tail = request->postfix;
 	}
-	list_del(&request->ring_link);
+	list_del_init(&request->ring_link);
 
-	request->ring->head = tail;
+	ring->head = tail;
 }
 
 static void free_capture_list(struct i915_request *request)
@@ -340,30 +343,84 @@ static void free_capture_list(struct i915_request *request)
 	}
 }
 
+static void __retire_engine_request(struct intel_engine_cs *engine,
+				    struct i915_request *rq)
+{
+	GEM_TRACE("%s(%s) fence %llx:%d, global=%d, current %d\n",
+		  __func__, engine->name,
+		  rq->fence.context, rq->fence.seqno,
+		  rq->global_seqno,
+		  intel_engine_get_seqno(engine));
+
+	GEM_BUG_ON(!i915_request_completed(rq));
+
+	local_irq_disable();
+
+	spin_lock(&engine->timeline->lock);
+	GEM_BUG_ON(!list_is_first(&rq->link, &engine->timeline->requests));
+	list_del_init(&rq->link);
+	spin_unlock(&engine->timeline->lock);
+
+	spin_lock(&rq->lock);
+	if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags))
+		dma_fence_signal_locked(&rq->fence);
+	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags))
+		intel_engine_cancel_signaling(rq);
+	if (rq->waitboost) {
+		GEM_BUG_ON(!atomic_read(&rq->i915->gt_pm.rps.num_waiters));
+		atomic_dec(&rq->i915->gt_pm.rps.num_waiters);
+	}
+	spin_unlock(&rq->lock);
+
+	local_irq_enable();
+
+	/*
+	 * The backing object for the context is done after switching to the
+	 * *next* context. Therefore we cannot retire the previous context until
+	 * the next context has already started running. However, since we
+	 * cannot take the required locks at i915_request_submit() we
+	 * defer the unpinning of the active context to now, retirement of
+	 * the subsequent request.
+	 */
+	if (engine->last_retired_context)
+		intel_context_unpin(engine->last_retired_context, engine);
+	engine->last_retired_context = rq->ctx;
+}
+
+static void __retire_engine_upto(struct intel_engine_cs *engine,
+				 struct i915_request *rq)
+{
+	struct i915_request *tmp;
+
+	if (list_empty(&rq->link))
+		return;
+
+	do {
+		tmp = list_first_entry(&engine->timeline->requests,
+				       typeof(*tmp), link);
+
+		GEM_BUG_ON(tmp->engine != engine);
+		__retire_engine_request(engine, tmp);
+	} while (tmp != rq);
+}
+
 static void i915_request_retire(struct i915_request *request)
 {
-	struct intel_engine_cs *engine = request->engine;
 	struct i915_gem_active *active, *next;
 
 	GEM_TRACE("%s fence %llx:%d, global=%d, current %d\n",
-		  engine->name,
+		  request->engine->name,
 		  request->fence.context, request->fence.seqno,
 		  request->global_seqno,
-		  intel_engine_get_seqno(engine));
+		  intel_engine_get_seqno(request->engine));
 
 	lockdep_assert_held(&request->i915->drm.struct_mutex);
 	GEM_BUG_ON(!i915_sw_fence_signaled(&request->submit));
 	GEM_BUG_ON(!i915_request_completed(request));
-	GEM_BUG_ON(!request->i915->gt.active_requests);
 
 	trace_i915_request_retire(request);
 
-	spin_lock_irq(&engine->timeline->lock);
-	list_del_init(&request->link);
-	spin_unlock_irq(&engine->timeline->lock);
-
 	advance_ring(request);
-
 	free_capture_list(request);
 
 	/*
@@ -399,29 +456,9 @@ static void i915_request_retire(struct i915_request *request)
 
 	/* Retirement decays the ban score as it is a sign of ctx progress */
 	atomic_dec_if_positive(&request->ctx->ban_score);
+	intel_context_unpin(request->ctx, request->engine);
 
-	/*
-	 * The backing object for the context is done after switching to the
-	 * *next* context. Therefore we cannot retire the previous context until
-	 * the next context has already started running. However, since we
-	 * cannot take the required locks at i915_request_submit() we
-	 * defer the unpinning of the active context to now, retirement of
-	 * the subsequent request.
-	 */
-	if (engine->last_retired_context)
-		intel_context_unpin(engine->last_retired_context, engine);
-	engine->last_retired_context = request->ctx;
-
-	spin_lock_irq(&request->lock);
-	if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags))
-		dma_fence_signal_locked(&request->fence);
-	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags))
-		intel_engine_cancel_signaling(request);
-	if (request->waitboost) {
-		GEM_BUG_ON(!atomic_read(&request->i915->gt_pm.rps.num_waiters));
-		atomic_dec(&request->i915->gt_pm.rps.num_waiters);
-	}
-	spin_unlock_irq(&request->lock);
+	__retire_engine_upto(request->engine, request);
 
 	unreserve_gt(request->i915);
 
@@ -431,18 +468,24 @@ static void i915_request_retire(struct i915_request *request)
 
 void i915_request_retire_upto(struct i915_request *rq)
 {
-	struct intel_engine_cs *engine = rq->engine;
+	struct intel_ring *ring = rq->ring;
 	struct i915_request *tmp;
 
+	GEM_TRACE("%s fence %llx:%d, global=%d, current %d\n",
+		  rq->engine->name,
+		  rq->fence.context, rq->fence.seqno,
+		  rq->global_seqno,
+		  intel_engine_get_seqno(rq->engine));
+
 	lockdep_assert_held(&rq->i915->drm.struct_mutex);
 	GEM_BUG_ON(!i915_request_completed(rq));
 
-	if (list_empty(&rq->link))
+	if (list_empty(&rq->ring_link))
 		return;
 
 	do {
-		tmp = list_first_entry(&engine->timeline->requests,
-				       typeof(*tmp), link);
+		tmp = list_first_entry(&ring->request_list,
+				       typeof(*tmp), ring_link);
 
 		i915_request_retire(tmp);
 	} while (tmp != rq);
@@ -651,9 +694,9 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
 	if (ret)
 		goto err_unreserve;
 
-	/* Move the oldest request to the slab-cache (if not in use!) */
-	rq = list_first_entry_or_null(&engine->timeline->requests,
-				      typeof(*rq), link);
+	/* Move our oldest request to the slab-cache (if not in use!) */
+	rq = list_first_entry_or_null(&ring->request_list,
+				      typeof(*rq), ring_link);
 	if (rq && i915_request_completed(rq))
 		i915_request_retire(rq);
 
@@ -771,6 +814,9 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
 	if (ret)
 		goto err_unwind;
 
+	/* Keep a second pin for the dual retirement along engine and ring */
+	__intel_context_pin(rq->ctx, engine);
+
 	/* Check that we didn't interrupt ourselves with a new request */
 	GEM_BUG_ON(rq->timeline->seqno != rq->fence.seqno);
 	return rq;
@@ -1357,38 +1403,30 @@ long i915_request_wait(struct i915_request *rq,
 	return timeout;
 }
 
-static void engine_retire_requests(struct intel_engine_cs *engine)
+static void ring_retire_requests(struct intel_ring *ring)
 {
 	struct i915_request *request, *next;
-	u32 seqno = intel_engine_get_seqno(engine);
-	LIST_HEAD(retire);
 
-	spin_lock_irq(&engine->timeline->lock);
 	list_for_each_entry_safe(request, next,
-				 &engine->timeline->requests, link) {
-		if (!i915_seqno_passed(seqno, request->global_seqno))
+				 &ring->request_list, ring_link) {
+		if (!i915_request_completed(request))
 			break;
 
-		list_move_tail(&request->link, &retire);
-	}
-	spin_unlock_irq(&engine->timeline->lock);
-
-	list_for_each_entry_safe(request, next, &retire, link)
 		i915_request_retire(request);
+	}
 }
 
 void i915_retire_requests(struct drm_i915_private *i915)
 {
-	struct intel_engine_cs *engine;
-	enum intel_engine_id id;
+	struct intel_ring *ring, *next;
 
 	lockdep_assert_held(&i915->drm.struct_mutex);
 
 	if (!i915->gt.active_requests)
 		return;
 
-	for_each_engine(engine, i915, id)
-		engine_retire_requests(engine);
+	list_for_each_entry_safe(ring, next, &i915->gt.rings, link)
+		ring_retire_requests(ring);
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)

drivers/gpu/drm/i915/i915_utils.h

@@ -120,6 +120,12 @@ static inline u64 ptr_to_u64(const void *ptr)
 
 #include <linux/list.h>
 
+static inline int list_is_first(const struct list_head *list,
+				const struct list_head *head)
+{
+	return head->next == list;
+}
+
 static inline void __list_del_many(struct list_head *head,
 				   struct list_head *first)
 {

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1066,7 +1066,6 @@ int intel_ring_pin(struct intel_ring *ring,
 
 void intel_ring_reset(struct intel_ring *ring, u32 tail)
 {
-	GEM_BUG_ON(!list_empty(&ring->request_list));
 	ring->tail = tail;
 	ring->head = tail;
 	ring->emit = tail;
@@ -1125,6 +1124,7 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size)
 
 	GEM_BUG_ON(!is_power_of_2(size));
 	GEM_BUG_ON(RING_CTL_SIZE(size) & ~RING_NR_PAGES);
+	lockdep_assert_held(&engine->i915->drm.struct_mutex);
 
 	ring = kzalloc(sizeof(*ring), GFP_KERNEL);
 	if (!ring)
@@ -1150,6 +1150,8 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size)
 	}
 	ring->vma = vma;
 
+	list_add(&ring->link, &engine->i915->gt.rings);
+
 	return ring;
 }
 
@@ -1161,6 +1163,8 @@ intel_ring_free(struct intel_ring *ring)
 	i915_vma_close(ring->vma);
 	__i915_gem_object_release_unless_active(obj);
 
+	list_del(&ring->link);
+
 	kfree(ring);
 }
 

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -130,6 +130,7 @@ struct intel_ring {
 	void *vaddr;
 
 	struct list_head request_list;
+	struct list_head link;
 
 	u32 head;
 	u32 tail;

drivers/gpu/drm/i915/selftests/mock_engine.c

@@ -147,9 +147,18 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
 	INIT_LIST_HEAD(&ring->request_list);
 	intel_ring_update_space(ring);
 
+	list_add(&ring->link, &engine->i915->gt.rings);
+
 	return ring;
 }
 
+static void mock_ring_free(struct intel_ring *ring)
+{
+	list_del(&ring->link);
+
+	kfree(ring);
+}
+
 struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 				    const char *name,
 				    int id)
@@ -162,12 +171,6 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 	if (!engine)
 		return NULL;
 
-	engine->base.buffer = mock_ring(&engine->base);
-	if (!engine->base.buffer) {
-		kfree(engine);
-		return NULL;
-	}
-
 	/* minimal engine setup for requests */
 	engine->base.i915 = i915;
 	snprintf(engine->base.name, sizeof(engine->base.name), "%s", name);
@@ -192,7 +195,16 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 	timer_setup(&engine->hw_delay, hw_delay_complete, 0);
 	INIT_LIST_HEAD(&engine->hw_queue);
 
+	engine->base.buffer = mock_ring(&engine->base);
+	if (!engine->base.buffer)
+		goto err_breadcrumbs;
+
 	return &engine->base;
+
+err_breadcrumbs:
+	intel_engine_fini_breadcrumbs(&engine->base);
+	kfree(engine);
+	return NULL;
 }
 
 void mock_engine_flush(struct intel_engine_cs *engine)
@@ -226,8 +238,9 @@ void mock_engine_free(struct intel_engine_cs *engine)
 	if (engine->last_retired_context)
 		intel_context_unpin(engine->last_retired_context, engine);
 
+	mock_ring_free(engine->buffer);
+
 	intel_engine_fini_breadcrumbs(engine);
 
-	kfree(engine->buffer);
 	kfree(engine);
 }