drm/ttm: rework pipelined eviction fence handling

Until now ttm stored a single pipelined eviction fence which means
drivers had to use a single entity for these evictions.

To lift this requirement, this commit allows up to 8 entities to
be used.

Ideally a dma_resv object would have been used as a container of
the eviction fences, but the locking rules makes it complex.
dma_resv all have the same ww_class, which means "Attempting to
lock more mutexes after ww_acquire_done." is an error.

One alternative considered was to introduced a 2nd ww_class for
specific resv to hold a single "transient" lock (= the resv lock
would only be held for a short period, without taking any other
locks).

The other option, is to statically reserve a fence array, and
extend the existing code to deal with N fences, instead of 1.

The driver is still responsible to reserve the correct number
of fence slots.

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Link: https://lore.kernel.org/r/20251121101315.3585-20-pierre-eric.pelloux-prayer@amd.com
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c

@@ -652,7 +652,7 @@ static void ttm_bo_validate_move_fence_signaled(struct kunit *test)
 	int err;
 
 	man = ttm_manager_type(priv->ttm_dev, mem_type);
-	man->move = dma_fence_get_stub();
+	man->eviction_fences[0] = dma_fence_get_stub();
 
 	bo = ttm_bo_kunit_init(test, test->priv, size, NULL);
 	bo->type = bo_type;
@@ -669,7 +669,7 @@ static void ttm_bo_validate_move_fence_signaled(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, ctx.bytes_moved, size);
 
 	ttm_bo_fini(bo);
-	dma_fence_put(man->move);
+	dma_fence_put(man->eviction_fences[0]);
 }
 
 static const struct ttm_bo_validate_test_case ttm_bo_validate_wait_cases[] = {
@@ -733,9 +733,9 @@ static void ttm_bo_validate_move_fence_not_signaled(struct kunit *test)
 
 	spin_lock_init(&fence_lock);
 	man = ttm_manager_type(priv->ttm_dev, fst_mem);
-	man->move = alloc_mock_fence(test);
+	man->eviction_fences[0] = alloc_mock_fence(test);
 
-	task = kthread_create(threaded_fence_signal, man->move, "move-fence-signal");
+	task = kthread_create(threaded_fence_signal, man->eviction_fences[0], "move-fence-signal");
 	if (IS_ERR(task))
 		KUNIT_FAIL(test, "Couldn't create move fence signal task\n");
 
@@ -743,7 +743,8 @@ static void ttm_bo_validate_move_fence_not_signaled(struct kunit *test)
 	err = ttm_bo_validate(bo, placement_val, &ctx_val);
 	dma_resv_unlock(bo->base.resv);
 
-	dma_fence_wait_timeout(man->move, false, MAX_SCHEDULE_TIMEOUT);
+	dma_fence_wait_timeout(man->eviction_fences[0], false, MAX_SCHEDULE_TIMEOUT);
+	man->eviction_fences[0] = NULL;
 
 	KUNIT_EXPECT_EQ(test, err, 0);
 	KUNIT_EXPECT_EQ(test, ctx_val.bytes_moved, size);

drivers/gpu/drm/ttm/tests/ttm_resource_test.c

@@ -207,6 +207,7 @@ static void ttm_resource_manager_init_basic(struct kunit *test)
 	struct ttm_resource_test_priv *priv = test->priv;
 	struct ttm_resource_manager *man;
 	size_t size = SZ_16K;
+	int i;
 
 	man = kunit_kzalloc(test, sizeof(*man), GFP_KERNEL);
 	KUNIT_ASSERT_NOT_NULL(test, man);
@@ -216,8 +217,8 @@ static void ttm_resource_manager_init_basic(struct kunit *test)
 	KUNIT_ASSERT_PTR_EQ(test, man->bdev, priv->devs->ttm_dev);
 	KUNIT_ASSERT_EQ(test, man->size, size);
 	KUNIT_ASSERT_EQ(test, man->usage, 0);
-	KUNIT_ASSERT_NULL(test, man->move);
-	KUNIT_ASSERT_NOT_NULL(test, &man->move_lock);
+	for (i = 0; i < TTM_NUM_MOVE_FENCES; i++)
+		KUNIT_ASSERT_NULL(test, man->eviction_fences[i]);
 
 	for (int i = 0; i < TTM_MAX_BO_PRIORITY; ++i)
 		KUNIT_ASSERT_TRUE(test, list_empty(&man->lru[i]));

drivers/gpu/drm/ttm/ttm_bo.c

@@ -659,34 +659,35 @@ void ttm_bo_unpin(struct ttm_buffer_object *bo)
 EXPORT_SYMBOL(ttm_bo_unpin);
 
 /*
- * Add the last move fence to the BO as kernel dependency and reserve a new
- * fence slot.
+ * Add the pipelined eviction fencesto the BO as kernel dependency and reserve new
+ * fence slots.
  */
-static int ttm_bo_add_move_fence(struct ttm_buffer_object *bo,
-				 struct ttm_resource_manager *man,
-				 bool no_wait_gpu)
+static int ttm_bo_add_pipelined_eviction_fences(struct ttm_buffer_object *bo,
+						struct ttm_resource_manager *man,
+						bool no_wait_gpu)
 {
 	struct dma_fence *fence;
-	int ret;
+	int i;
 
-	spin_lock(&man->move_lock);
-	fence = dma_fence_get(man->move);
-	spin_unlock(&man->move_lock);
+	spin_lock(&man->eviction_lock);
+	for (i = 0; i < TTM_NUM_MOVE_FENCES; i++) {
+		fence = man->eviction_fences[i];
+		if (!fence)
+			continue;
 
-	if (!fence)
-		return 0;
-
-	if (no_wait_gpu) {
-		ret = dma_fence_is_signaled(fence) ? 0 : -EBUSY;
-		dma_fence_put(fence);
-		return ret;
+		if (no_wait_gpu) {
+			if (!dma_fence_is_signaled(fence)) {
+				spin_unlock(&man->eviction_lock);
+				return -EBUSY;
+			}
+		} else {
+			dma_resv_add_fence(bo->base.resv, fence, DMA_RESV_USAGE_KERNEL);
+		}
 	}
+	spin_unlock(&man->eviction_lock);
 
-	dma_resv_add_fence(bo->base.resv, fence, DMA_RESV_USAGE_KERNEL);
-
-	ret = dma_resv_reserve_fences(bo->base.resv, 1);
-	dma_fence_put(fence);
-	return ret;
+	/* TODO: this call should be removed. */
+	return dma_resv_reserve_fences(bo->base.resv, 1);
 }
 
 /**
@@ -719,7 +720,7 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
 	int i, ret;
 
 	ticket = dma_resv_locking_ctx(bo->base.resv);
-	ret = dma_resv_reserve_fences(bo->base.resv, 1);
+	ret = dma_resv_reserve_fences(bo->base.resv, TTM_NUM_MOVE_FENCES);
 	if (unlikely(ret))
 		return ret;
 
@@ -758,7 +759,7 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
 				return ret;
 		}
 
-		ret = ttm_bo_add_move_fence(bo, man, ctx->no_wait_gpu);
+		ret = ttm_bo_add_pipelined_eviction_fences(bo, man, ctx->no_wait_gpu);
 		if (unlikely(ret)) {
 			ttm_resource_free(bo, res);
 			if (ret == -EBUSY)

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -258,7 +258,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	ret = dma_resv_trylock(&fbo->base.base._resv);
 	WARN_ON(!ret);
 
-	ret = dma_resv_reserve_fences(&fbo->base.base._resv, 1);
+	ret = dma_resv_reserve_fences(&fbo->base.base._resv, TTM_NUM_MOVE_FENCES);
 	if (ret) {
 		dma_resv_unlock(&fbo->base.base._resv);
 		kfree(fbo);
@@ -646,20 +646,44 @@ static void ttm_bo_move_pipeline_evict(struct ttm_buffer_object *bo,
 {
 	struct ttm_device *bdev = bo->bdev;
 	struct ttm_resource_manager *from;
+	struct dma_fence *tmp;
+	int i;
 
 	from = ttm_manager_type(bdev, bo->resource->mem_type);
 
 	/**
 	 * BO doesn't have a TTM we need to bind/unbind. Just remember
-	 * this eviction and free up the allocation
+	 * this eviction and free up the allocation.
+	 * The fence will be saved in the first free slot or in the slot
+	 * already used to store a fence from the same context. Since
+	 * drivers can't use more than TTM_NUM_MOVE_FENCES contexts for
+	 * evictions we should always find a slot to use.
 	 */
-	spin_lock(&from->move_lock);
-	if (!from->move || dma_fence_is_later(fence, from->move)) {
-		dma_fence_put(from->move);
-		from->move = dma_fence_get(fence);
+	spin_lock(&from->eviction_lock);
+	for (i = 0; i < TTM_NUM_MOVE_FENCES; i++) {
+		tmp = from->eviction_fences[i];
+		if (!tmp)
+			break;
+		if (fence->context != tmp->context)
+			continue;
+		if (dma_fence_is_later(fence, tmp)) {
+			dma_fence_put(tmp);
+			break;
+		}
+		goto unlock;
+	}
+	if (i < TTM_NUM_MOVE_FENCES) {
+		from->eviction_fences[i] = dma_fence_get(fence);
+	} else {
+		WARN(1, "not enough fence slots for all fence contexts");
+		spin_unlock(&from->eviction_lock);
+		dma_fence_wait(fence, false);
+		goto end;
 	}
-	spin_unlock(&from->move_lock);
 
+unlock:
+	spin_unlock(&from->eviction_lock);
+end:
 	ttm_resource_free(bo, &bo->resource);
 }
 

drivers/gpu/drm/ttm/ttm_resource.c

@@ -524,14 +524,15 @@ void ttm_resource_manager_init(struct ttm_resource_manager *man,
 {
 	unsigned i;
 
-	spin_lock_init(&man->move_lock);
 	man->bdev = bdev;
 	man->size = size;
 	man->usage = 0;
 
 	for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i)
 		INIT_LIST_HEAD(&man->lru[i]);
-	man->move = NULL;
+	spin_lock_init(&man->eviction_lock);
+	for (i = 0; i < TTM_NUM_MOVE_FENCES; i++)
+		man->eviction_fences[i] = NULL;
 }
 EXPORT_SYMBOL(ttm_resource_manager_init);
 
@@ -552,7 +553,7 @@ int ttm_resource_manager_evict_all(struct ttm_device *bdev,
 		.no_wait_gpu = false,
 	};
 	struct dma_fence *fence;
-	int ret;
+	int ret, i;
 
 	do {
 		ret = ttm_bo_evict_first(bdev, man, &ctx);
@@ -562,18 +563,24 @@ int ttm_resource_manager_evict_all(struct ttm_device *bdev,
 	if (ret && ret != -ENOENT)
 		return ret;
 
-	spin_lock(&man->move_lock);
-	fence = dma_fence_get(man->move);
-	spin_unlock(&man->move_lock);
+	ret = 0;
 
-	if (fence) {
-		ret = dma_fence_wait(fence, false);
-		dma_fence_put(fence);
-		if (ret)
-			return ret;
+	spin_lock(&man->eviction_lock);
+	for (i = 0; i < TTM_NUM_MOVE_FENCES; i++) {
+		fence = man->eviction_fences[i];
+		if (fence && !dma_fence_is_signaled(fence)) {
+			dma_fence_get(fence);
+			spin_unlock(&man->eviction_lock);
+			ret = dma_fence_wait(fence, false);
+			dma_fence_put(fence);
+			if (ret)
+				return ret;
+			spin_lock(&man->eviction_lock);
+		}
 	}
+	spin_unlock(&man->eviction_lock);
 
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(ttm_resource_manager_evict_all);
 

include/drm/ttm/ttm_resource.h

@@ -51,6 +51,15 @@ struct io_mapping;
 struct sg_table;
 struct scatterlist;
 
+/**
+ * define TTM_NUM_MOVE_FENCES - How many entities can be used for evictions
+ *
+ * Pipelined evictions can be spread on multiple entities. This
+ * is the max number of entities that can be used by the driver
+ * for that purpose.
+ */
+#define TTM_NUM_MOVE_FENCES 8
+
 /**
  * enum ttm_lru_item_type - enumerate ttm_lru_item subclasses
  */
@@ -181,8 +190,8 @@ struct ttm_resource_manager_func {
  * @size: Size of the managed region.
  * @bdev: ttm device this manager belongs to
  * @func: structure pointer implementing the range manager. See above
- * @move_lock: lock for move fence
- * @move: The fence of the last pipelined move operation.
+ * @eviction_lock: lock for eviction fences
+ * @eviction_fences: The fences of the last pipelined move operation.
  * @lru: The lru list for this memory type.
  *
  * This structure is used to identify and manage memory types for a device.
@@ -196,12 +205,12 @@ struct ttm_resource_manager {
 	struct ttm_device *bdev;
 	uint64_t size;
 	const struct ttm_resource_manager_func *func;
-	spinlock_t move_lock;
 
-	/*
-	 * Protected by @move_lock.
+	/* This is very similar to a dma_resv object, but locking rules make
+	 * it difficult to use one in this context.
 	 */
-	struct dma_fence *move;
+	spinlock_t eviction_lock;
+	struct dma_fence *eviction_fences[TTM_NUM_MOVE_FENCES];
 
 	/*
 	 * Protected by the bdev->lru_lock.
@@ -422,8 +431,12 @@ static inline bool ttm_resource_manager_used(struct ttm_resource_manager *man)
 static inline void
 ttm_resource_manager_cleanup(struct ttm_resource_manager *man)
 {
-	dma_fence_put(man->move);
-	man->move = NULL;
+	int i;
+
+	for (i = 0; i < TTM_NUM_MOVE_FENCES; i++) {
+		dma_fence_put(man->eviction_fences[i]);
+		man->eviction_fences[i] = NULL;
+	}
 }
 
 void ttm_lru_bulk_move_init(struct ttm_lru_bulk_move *bulk);