[Linaro-mm-sig] Re: [PATCH v1 02/20] drm/ttm: rework pipelined eviction fence handling

On 11/4/25 09:35, Pierre-Eric Pelloux-Prayer wrote:

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.

Lastly ttm_resource_manager.pipelined_eviction.n_fences is initialized to 1, so the new behavior is opt-in.

Signed-off-by: Pierre-Eric Pelloux-Prayer pierre-eric.pelloux-prayer@amd.com

drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 8 ++- .../gpu/drm/ttm/tests/ttm_bo_validate_test.c | 13 +++-- drivers/gpu/drm/ttm/tests/ttm_resource_test.c | 5 +- drivers/gpu/drm/ttm/ttm_bo.c | 56 ++++++++++++------- drivers/gpu/drm/ttm/ttm_bo_util.c | 36 ++++++++++-- drivers/gpu/drm/ttm/ttm_resource.c | 45 ++++++++++----- include/drm/ttm/ttm_resource.h | 34 ++++++++--- 7 files changed, 139 insertions(+), 58 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c index 326476089db3..c66f00434991 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c @@ -2156,7 +2156,7 @@ void amdgpu_ttm_set_buffer_funcs_status(struct amdgpu_device *adev, bool enable) { struct ttm_resource_manager *man = ttm_manager_type(&adev->mman.bdev, TTM_PL_VRAM); uint64_t size;

• int r;

• int r, i;

if (!adev->mman.initialized || amdgpu_in_reset(adev) || adev->mman.buffer_funcs_enabled == enable || adev->gmc.is_app_apu) @@ -2190,8 +2190,10 @@ void amdgpu_ttm_set_buffer_funcs_status(struct amdgpu_device *adev, bool enable) } else { drm_sched_entity_destroy(&adev->mman.high_pr); drm_sched_entity_destroy(&adev->mman.low_pr);

• dma_fence_put(man->move);
  

• man->move = NULL;
  

• for (i = 0; i < TTM_FENCES_MAX_SLOT_COUNT; i++) {
  

• 	dma_fence_put(man->pipelined_eviction.fences[i]);
  

• 	man->pipelined_eviction.fences[i] = NULL;
  

• }
  

  }

/* this just adjusts TTM size idea, which sets lpfn to the correct value */ diff --git a/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c b/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c index 3148f5d3dbd6..1396674e1923 100644 --- a/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c +++ b/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c @@ -651,7 +651,8 @@ 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->pipelined_eviction.n_fences = 1;
• man->pipelined_eviction.fences[0] = dma_fence_get_stub();

bo = ttm_bo_kunit_init(test, test->priv, size, NULL); bo->type = bo_type; @@ -668,7 +669,7 @@ static void ttm_bo_validate_move_fence_signaled(struct kunit *test) KUNIT_EXPECT_EQ(test, ctx.bytes_moved, size); ttm_bo_put(bo);

• dma_fence_put(man->move);

• dma_fence_put(man->pipelined_eviction.fences[0]);

} static const struct ttm_bo_validate_test_case ttm_bo_validate_wait_cases[] = { @@ -732,9 +733,10 @@ 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->pipelined_eviction.n_fences = 1;
• man->pipelined_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->pipelined_eviction.fences[0], "move-fence-signal"); if (IS_ERR(task)) KUNIT_FAIL(test, "Couldn't create move fence signal task\n");

@@ -742,7 +744,8 @@ 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->pipelined_eviction.fences[0], false, MAX_SCHEDULE_TIMEOUT);
• man->pipelined_eviction.fences[0] = NULL;

KUNIT_EXPECT_EQ(test, err, 0); KUNIT_EXPECT_EQ(test, ctx_val.bytes_moved, size); diff --git a/drivers/gpu/drm/ttm/tests/ttm_resource_test.c b/drivers/gpu/drm/ttm/tests/ttm_resource_test.c index e6ea2bd01f07..6dfdf759a491 100644 --- a/drivers/gpu/drm/ttm/tests/ttm_resource_test.c +++ b/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_FENCES_MAX_SLOT_COUNT; i++)

• KUNIT_ASSERT_NULL(test, man->pipelined_eviction.fences[i]);
  

for (int i = 0; i < TTM_MAX_BO_PRIORITY; ++i) KUNIT_ASSERT_TRUE(test, list_empty(&man->lru[i])); diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c index f4d9e68b21e7..bc6d4a6c6d70 100644 --- a/drivers/gpu/drm/ttm/ttm_bo.c +++ b/drivers/gpu/drm/ttm/ttm_bo.c @@ -658,34 +658,48 @@ 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 *fences_to_add[TTM_FENCES_MAX_SLOT_COUNT] = {}; struct dma_fence *fence;

• int ret;

• bool all_signaled = true, signaled;
• int i, n = 0;

• spin_lock(&man->move_lock);
• fence = dma_fence_get(man->move);
• spin_unlock(&man->move_lock);

• spin_lock(&man->pipelined_eviction.lock);
• for (i = 0; i < man->pipelined_eviction.n_fences; i++) {

• fence = man->pipelined_eviction.fences[i];
  

• if (!fence)
  

• 	continue;
  

• signaled = dma_fence_is_signaled(fence);
  

• if (!fence)

• if (signaled) {
  

• 	dma_fence_put(man->pipelined_eviction.fences[i]);
  

• 	man->pipelined_eviction.fences[i] = NULL;
  

Please completely drop that, only check if the fences are signaled when the no_wait_gpu flag is set.

• } else {
  

• 	all_signaled = false;
  

• 	if (no_wait_gpu) {
  

• 		spin_unlock(&man->pipelined_eviction.lock);
  

• 		return -EBUSY;
  

• 	}
  

• 	fences_to_add[n++] = dma_fence_get(fence);
  

• }
  

• }
• spin_unlock(&man->pipelined_eviction.lock);
• if (all_signaled) return 0;

• if (no_wait_gpu) {

• ret = dma_fence_is_signaled(fence) ? 0 : -EBUSY;
  

• dma_fence_put(fence);
  

• return ret;
  

• for (i = 0; i < n; i++) {

• dma_resv_add_fence(bo->base.resv, fences_to_add[i], DMA_RESV_USAGE_KERNEL);
  

• dma_fence_put(fences_to_add[i]);
  

  }

• 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;

• return dma_resv_reserve_fences(bo->base.resv, TTM_FENCES_MAX_SLOT_COUNT);

Please separate out a patch where the call to dma_resv_reserve_fences() is removed here.

} /** @@ -718,7 +732,7 @@ 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_FENCES_MAX_SLOT_COUNT); if (unlikely(ret)) return ret;

@@ -757,7 +771,7 @@ 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)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c index acbbca9d5c92..ada8af965acf 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_util.c +++ b/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_FENCES_MAX_SLOT_COUNT); if (ret) { dma_resv_unlock(&fbo->base.base._resv); kfree(fbo);

@@ -646,6 +646,8 @@ 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, free_slot = -1;

from = ttm_manager_type(bdev, bo->resource->mem_type); @@ -653,13 +655,35 @@ static void ttm_bo_move_pipeline_evict(struct ttm_buffer_object *bo, * BO doesn't have a TTM we need to bind/unbind. Just remember * this eviction and free up the allocation */

• 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->pipelined_eviction.lock);
• for (i = 0; i < from->pipelined_eviction.n_fences; i++) {

• tmp = from->pipelined_eviction.fences[i];
  

• if (!tmp) {
  

• 	if (free_slot < 0)
  

• 		free_slot = i;
  

• 	continue;
  

Just break here.

• }
  

• if (fence->context != tmp->context)
  

• 	continue;
  

• if (dma_fence_is_later(fence, tmp)) {
  

• 	dma_fence_put(tmp);
  

• 	free_slot = i;
  

• 	break;
  

• }
  

• goto unlock;
  

• }
• if (free_slot >= 0) {

Drop free_slot and check i here.

• from->pipelined_eviction.fences[free_slot] = dma_fence_get(fence);
  

• } else {

• WARN(1, "not enough fence slots for all fence contexts");
  

• spin_unlock(&from->pipelined_eviction.lock);
  

• dma_fence_wait(fence, false);
  

• goto end;
  

  }

• spin_unlock(&from->move_lock);

+unlock:

• spin_unlock(&from->pipelined_eviction.lock);

+end: ttm_resource_free(bo, &bo->resource); } diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c index e2c82ad07eb4..ae0d4621cc55 100644 --- a/drivers/gpu/drm/ttm/ttm_resource.c +++ b/drivers/gpu/drm/ttm/ttm_resource.c @@ -523,14 +523,19 @@ 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->pipelined_eviction.lock);
• for (i = 0; i < TTM_FENCES_MAX_SLOT_COUNT; i++)

• man->pipelined_eviction.fences[i] = NULL;
  

• /* Can be overridden by drivers that wants to use more than 1 entity

• * for moves and evictions (limited to TTM_FENCES_MAX_SLOT_COUNT).
  

• */
  

• man->pipelined_eviction.n_fences = 1;

} EXPORT_SYMBOL(ttm_resource_manager_init); @@ -551,7 +556,7 @@ 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); @@ -561,18 +566,32 @@ 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;
  

• }

• do {

• fence = NULL;
  

• return 0;

• spin_lock(&man->pipelined_eviction.lock);
  

• for (i = 0; i < man->pipelined_eviction.n_fences; i++) {
  

• 	fence = man->pipelined_eviction.fences[i];
  

• 	man->pipelined_eviction.fences[i] = NULL;
  

Drop that. We should never set man->pipelined_eviction.fences to NULL.

Potentially even initialize all move fences with a stub fence.

• 	if (fence)
  

• 		break;
  

• }
  

• spin_unlock(&man->pipelined_eviction.lock);
  

• if (fence) {
  

• 	ret = dma_fence_wait(fence, false);
  

• 	dma_fence_put(fence);
  

• 	if (ret)
  

• 		break;
  

• } else {
  

• 	break;
  

• }
  

• } while (1);
• return ret;

} EXPORT_SYMBOL(ttm_resource_manager_evict_all); diff --git a/include/drm/ttm/ttm_resource.h b/include/drm/ttm/ttm_resource.h index f49daa504c36..898c429b37ad 100644 --- a/include/drm/ttm/ttm_resource.h +++ b/include/drm/ttm/ttm_resource.h @@ -50,6 +50,15 @@ struct io_mapping; struct sg_table; struct scatterlist; +/**

• • define TTM_FENCES_MAX_SLOT_COUNT - 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_FENCES_MAX_SLOT_COUNT 8

Make that TTM_NUM_MOVE_FENCES.

/**

• enum ttm_lru_item_type - enumerate ttm_lru_item subclasses

*/ @@ -180,8 +189,10 @@ 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.

• • @pipelined_eviction.lock: lock for eviction fences
• • @pipelined_eviction.n_fences: The number of fences allowed in the array. If
• • 0, pipelined evictions aren't used.
• • @pipelined_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.

@@ -195,12 +206,15 @@ 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 a it in this context.
  

  */

• struct dma_fence *move;

• struct {

• spinlock_t lock;
  

• int n_fences;
  

• struct dma_fence *fences[TTM_FENCES_MAX_SLOT_COUNT];
  

• } pipelined_eviction;

Drop the separate structure, just make move an array instead.

And also drop n_fences. Just always take a look at all fences.

Regards, Christian.

/* * Protected by the bdev->lru_lock. @@ -421,8 +435,12 @@ 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_FENCES_MAX_SLOT_COUNT; i++) {

• dma_fence_put(man->pipelined_eviction.fences[i]);
  

• man->pipelined_eviction.fences[i] = NULL;
  

• }

} void ttm_lru_bulk_move_init(struct ttm_lru_bulk_move *bulk);