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DKIM-Signature: v=1; a=ed25519-sha256; s=202408e; d=damsy.net; c=relaxed/relaxed; h=From:To:Subject:Date:Message-ID; t=1762338897; bh=bqBYiyWlxDUdnNgsJSqCOZI JNIvP50J9OOyodzXZMwQ=; b=qtLmukZvlE5csXU0v+0rrz6psZY9zFMr/pFXe28NibTMUSMaPl bNMt/xHjnuzYZl1fUg49oVa9LiTlMlt0U+BA==; Message-ID: <5bf372ea-40ef-4b07-be13-53451828d3e1@damsy.net> Date: Wed, 5 Nov 2025 11:34:56 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 02/20] drm/ttm: rework pipelined eviction fence handling To: =?UTF-8?Q?Christian_K=C3=B6nig?= , Pierre-Eric Pelloux-Prayer , Alex Deucher , David Airlie , Simona Vetter , Huang Rui , Matthew Auld , Matthew Brost , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Sumit Semwal Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org References: <20251104083605.13677-1-pierre-eric.pelloux-prayer@amd.com> <20251104083605.13677-3-pierre-eric.pelloux-prayer@amd.com> <13f0cda3-baae-42a4-a7c6-1fdd774bb5d2@amd.com> Content-Language: en-US From: Pierre-Eric Pelloux-Prayer In-Reply-To: <13f0cda3-baae-42a4-a7c6-1fdd774bb5d2@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Le 04/11/2025 à 15:12, Christian König a écrit : > 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 >> --- >> 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. ok. > >> + } 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. Can you remind me why it's not needed? > >> } >> >> /** >> @@ -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. The logic here is to reuse context slots. Even if slot 0 is empty, I need to use slot 1 if slot 1's context is the same as fence->context. This way, we're guaranteed to find a slot for all contexts used by the driver. > >> + } >> + 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. Why? > > 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. Ok. > >> + >> /** >> * 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. IMO pipelined_eviction.fences and pipelined_eviction.lock is clearer when reading the code than moves and move_lock but if you prefer I'll switch back to the old names. > > And also drop n_fences. Just always take a look at all fences. OK. Thanks, Pierre-Eric > > 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);