Re: [PATCH v2 04/20] drm/amdgpu: introduce amdgpu_ttm_buffer_entity

Fri, 14 Nov 2025 12:19:00 -0800 

On 2025-11-14 07:57, Christian König wrote:

On 11/13/25 17:05, Pierre-Eric Pelloux-Prayer wrote:

No functional change for now, but this struct will have more
fields added in the next commit.

Technically the change introduces synchronisation issue, because
dependencies between successive jobs are not taken care of
properly. For instance, amdgpu_ttm_clear_buffer uses
amdgpu_ttm_map_buffer then amdgpu_ttm_fill_mem which use
different entities (default_entity then move/clear entity).
But it's all working as expected, because all entities use the
same sdma instance for now and default_entity has a higher prio
so its job always gets scheduler first.

The next commits will deal with these dependencies correctly.

---
v2: renamed amdgpu_ttm_buffer_entity
---

Signed-off-by: Pierre-Eric Pelloux-Prayer <[email protected]>

Reviewed-by: Christian König <[email protected]>


---
  drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c  |  2 +-
  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c  | 30 +++++++++++++++++-------
  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h  | 12 ++++++----
  drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 13 ++++++----
  4 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
index 9dcf51991b5b..8e2d41c9c271 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
@@ -687,7 +687,7 @@ void amdgpu_gmc_flush_gpu_tlb(struct amdgpu_device *adev, 
uint32_t vmid,
         * itself at least for GART.
         */
        mutex_lock(&adev->mman.gtt_window_lock);
-       r = amdgpu_job_alloc_with_ib(ring->adev, &adev->mman.high_pr,
+       r = amdgpu_job_alloc_with_ib(ring->adev, 
&adev->mman.default_entity.base,
                                     AMDGPU_FENCE_OWNER_UNDEFINED,
                                     16 * 4, AMDGPU_IB_POOL_IMMEDIATE,
                                     &job, AMDGPU_KERNEL_JOB_ID_FLUSH_GPU_TLB);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index c985f57fa227..42d448cd6a6d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -224,7 +224,7 @@ static int amdgpu_ttm_map_buffer(struct ttm_buffer_object 
*bo,
        num_dw = ALIGN(adev->mman.buffer_funcs->copy_num_dw, 8);
        num_bytes = num_pages * 8 * AMDGPU_GPU_PAGES_IN_CPU_PAGE;
- r = amdgpu_job_alloc_with_ib(adev, &adev->mman.high_pr, 
+       r = amdgpu_job_alloc_with_ib(adev, &adev->mman.default_entity.base,
                                     AMDGPU_FENCE_OWNER_UNDEFINED,
                                     num_dw * 4 + num_bytes,
                                     AMDGPU_IB_POOL_DELAYED, &job,
@@ -1486,7 +1486,7 @@ static int amdgpu_ttm_access_memory_sdma(struct 
ttm_buffer_object *bo,
                memcpy(adev->mman.sdma_access_ptr, buf, len);
num_dw = ALIGN(adev->mman.buffer_funcs->copy_num_dw, 8); 
-       r = amdgpu_job_alloc_with_ib(adev, &adev->mman.high_pr,
+       r = amdgpu_job_alloc_with_ib(adev, &adev->mman.default_entity.base,
                                     AMDGPU_FENCE_OWNER_UNDEFINED,
                                     num_dw * 4, AMDGPU_IB_POOL_DELAYED,
                                     &job,
@@ -2168,7 +2168,7 @@ void amdgpu_ttm_set_buffer_funcs_status(struct 
amdgpu_device *adev, bool enable)
ring = adev->mman.buffer_funcs_ring; 
                sched = &ring->sched;
-               r = drm_sched_entity_init(&adev->mman.high_pr,
+               r = drm_sched_entity_init(&adev->mman.default_entity.base,
                                          DRM_SCHED_PRIORITY_KERNEL, &sched,
                                          1, NULL);
                if (r) {
@@ -2178,18 +2178,30 @@ void amdgpu_ttm_set_buffer_funcs_status(struct 
amdgpu_device *adev, bool enable)
                        return;
                }
- r = drm_sched_entity_init(&adev->mman.low_pr, 
+               r = drm_sched_entity_init(&adev->mman.clear_entity.base,
+                                         DRM_SCHED_PRIORITY_NORMAL, &sched,
+                                         1, NULL);
+               if (r) {
+                       dev_err(adev->dev,
+                               "Failed setting up TTM BO clear entity (%d)\n",
+                               r);
+                       goto error_free_entity;
+               }
+
+               r = drm_sched_entity_init(&adev->mman.move_entity.base,
                                          DRM_SCHED_PRIORITY_NORMAL, &sched,
                                          1, NULL);
                if (r) {
                        dev_err(adev->dev,
                                "Failed setting up TTM BO move entity (%d)\n",
                                r);
+                       drm_sched_entity_destroy(&adev->mman.clear_entity.base);
                        goto error_free_entity;
                }
        } else {
-               drm_sched_entity_destroy(&adev->mman.high_pr);
-               drm_sched_entity_destroy(&adev->mman.low_pr);
+               drm_sched_entity_destroy(&adev->mman.default_entity.base);
+               drm_sched_entity_destroy(&adev->mman.clear_entity.base);
+               drm_sched_entity_destroy(&adev->mman.move_entity.base);
                for (i = 0; i < TTM_NUM_MOVE_FENCES; i++) {
                        dma_fence_put(man->eviction_fences[i]);
                        man->eviction_fences[i] = NULL;
@@ -2207,7 +2219,7 @@ void amdgpu_ttm_set_buffer_funcs_status(struct 
amdgpu_device *adev, bool enable)
        return;
error_free_entity: 
-       drm_sched_entity_destroy(&adev->mman.high_pr);
+       drm_sched_entity_destroy(&adev->mman.default_entity.base);
  }
static int amdgpu_ttm_prepare_job(struct amdgpu_device *adev, 
@@ -2219,8 +2231,8 @@ static int amdgpu_ttm_prepare_job(struct amdgpu_device 
*adev,
  {
        enum amdgpu_ib_pool_type pool = AMDGPU_IB_POOL_DELAYED;
        int r;
-       struct drm_sched_entity *entity = delayed ? &adev->mman.low_pr :
-                                                   &adev->mman.high_pr;
+       struct drm_sched_entity *entity = delayed ? 
&adev->mman.clear_entity.base :
+                                                   
&adev->mman.move_entity.base;
        r = amdgpu_job_alloc_with_ib(adev, entity,
                                     AMDGPU_FENCE_OWNER_UNDEFINED,
                                     num_dw * 4, pool, job, k_job_id);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
index 50e40380fe95..d2295d6c2b67 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
@@ -52,6 +52,10 @@ struct amdgpu_gtt_mgr {
        spinlock_t lock;
  };
+struct amdgpu_ttm_buffer_entity { 
+       struct drm_sched_entity base;
+};
+
  struct amdgpu_mman {
        struct ttm_device               bdev;
        struct ttm_pool                 *ttm_pools;
@@ -64,10 +68,10 @@ struct amdgpu_mman {
        bool                                    buffer_funcs_enabled;
struct mutex gtt_window_lock; 
-       /* High priority scheduler entity for buffer moves */
-       struct drm_sched_entity                 high_pr;
-       /* Low priority scheduler entity for VRAM clearing */
-       struct drm_sched_entity                 low_pr;
+
+       struct amdgpu_ttm_buffer_entity default_entity;
+       struct amdgpu_ttm_buffer_entity clear_entity;
+       struct amdgpu_ttm_buffer_entity move_entity;
struct amdgpu_vram_mgr vram_mgr; 
        struct amdgpu_gtt_mgr gtt_mgr;
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c 
b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
index 378af0b2aaa9..d74ff6e90590 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
@@ -45,7 +45,9 @@ svm_migrate_direct_mapping_addr(struct amdgpu_device *adev, 
u64 addr)
  }
static int 
-svm_migrate_gart_map(struct amdgpu_ring *ring, u64 npages,
+svm_migrate_gart_map(struct amdgpu_ring *ring,
+                    struct amdgpu_ttm_buffer_entity *entity,


Do we still need the ring parameter, or is that implied by the entity?

Other than that, the patch is

Acked-by: Felix Kuehling <[email protected]>



+                    u64 npages,
                     dma_addr_t *addr, u64 *gart_addr, u64 flags)
  {
        struct amdgpu_device *adev = ring->adev;
@@ -63,7 +65,7 @@ svm_migrate_gart_map(struct amdgpu_ring *ring, u64 npages,
        num_dw = ALIGN(adev->mman.buffer_funcs->copy_num_dw, 8);
        num_bytes = npages * 8;
- r = amdgpu_job_alloc_with_ib(adev, &adev->mman.high_pr, 
+       r = amdgpu_job_alloc_with_ib(adev, &entity->base,
                                     AMDGPU_FENCE_OWNER_UNDEFINED,
                                     num_dw * 4 + num_bytes,
                                     AMDGPU_IB_POOL_DELAYED,
@@ -128,11 +130,14 @@ svm_migrate_copy_memory_gart(struct amdgpu_device *adev, 
dma_addr_t *sys,
  {
        const u64 GTT_MAX_PAGES = AMDGPU_GTT_MAX_TRANSFER_SIZE;
        struct amdgpu_ring *ring = adev->mman.buffer_funcs_ring;
+       struct amdgpu_ttm_buffer_entity *entity;
        u64 gart_s, gart_d;
        struct dma_fence *next;
        u64 size;
        int r;
+ entity = &adev->mman.move_entity; 
+
        mutex_lock(&adev->mman.gtt_window_lock);
while (npages) { 
@@ -140,10 +145,10 @@ svm_migrate_copy_memory_gart(struct amdgpu_device *adev, 
dma_addr_t *sys,
if (direction == FROM_VRAM_TO_RAM) { 
                        gart_s = svm_migrate_direct_mapping_addr(adev, *vram);
-                       r = svm_migrate_gart_map(ring, size, sys, &gart_d, 0);
+                       r = svm_migrate_gart_map(ring, entity, size, sys, 
&gart_d, 0);
} else if (direction == FROM_RAM_TO_VRAM) { 
-                       r = svm_migrate_gart_map(ring, size, sys, &gart_s,
+                       r = svm_migrate_gart_map(ring, entity, size, sys, 
&gart_s,
                                                 KFD_IOCTL_SVM_FLAG_GPU_RO);
                        gart_d = svm_migrate_direct_mapping_addr(adev, *vram);
                }

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