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Subject[PATCH 09/11] drm/amdgpu: reuse VMIDs assigned to a VM only if there is also a free one
Date
From: Christian König <christian.koenig@amd.com>

This fixes a fairness problem with the GPU scheduler. VM having lot of
jobs could previously starve VM with less jobs.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 113 +++++++++++++++++----------------
1 file changed, 59 insertions(+), 54 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index b6484a2..f206820 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -179,75 +179,80 @@ int amdgpu_vm_grab_id(struct amdgpu_vm *vm, struct amdgpu_ring *ring,
uint64_t pd_addr = amdgpu_bo_gpu_offset(vm->page_directory);
struct amdgpu_device *adev = ring->adev;
struct fence *updates = sync->last_vm_update;
- struct amdgpu_vm_id *id;
+ struct amdgpu_vm_id *id, *idle;
unsigned i = ring->idx;
int r;

mutex_lock(&adev->vm_manager.lock);

- /* Check if we can use a VMID already assigned to this VM */
- do {
- struct fence *flushed;
-
- id = vm->ids[i++];
- if (i == AMDGPU_MAX_RINGS)
- i = 0;
-
- /* Check all the prerequisites to using this VMID */
- if (!id)
- continue;
-
- if (atomic64_read(&id->owner) != vm->client_id)
- continue;
-
- if (pd_addr != id->pd_gpu_addr)
- continue;
+ /* Check if we have an idle VMID */
+ list_for_each_entry(idle, &adev->vm_manager.ids_lru, list) {
+ if (amdgpu_sync_is_idle(&idle->active, ring))
+ break;

- if (id->last_user != ring &&
- (!id->last_flush || !fence_is_signaled(id->last_flush)))
- continue;
+ }

- flushed = id->flushed_updates;
- if (updates && (!flushed || fence_is_later(updates, flushed)))
- continue;
+ /* If we can't find a idle VMID to use, just wait for the oldest */
+ if (&idle->list == &adev->vm_manager.ids_lru) {
+ id = list_first_entry(&adev->vm_manager.ids_lru,
+ struct amdgpu_vm_id,
+ list);
+ } else {
+ /* Check if we can use a VMID already assigned to this VM */
+ do {
+ struct fence *flushed;
+
+ id = vm->ids[i++];
+ if (i == AMDGPU_MAX_RINGS)
+ i = 0;
+
+ /* Check all the prerequisites to using this VMID */
+ if (!id)
+ continue;
+
+ if (atomic64_read(&id->owner) != vm->client_id)
+ continue;
+
+ if (pd_addr != id->pd_gpu_addr)
+ continue;
+
+ if (id->last_user != ring && (!id->last_flush ||
+ !fence_is_signaled(id->last_flush)))
+ continue;
+
+ flushed = id->flushed_updates;
+ if (updates && (!flushed ||
+ fence_is_later(updates, flushed)))
+ continue;
+
+ /* Good we can use this VMID */
+ if (id->last_user == ring) {
+ r = amdgpu_sync_fence(ring->adev, sync,
+ id->first);
+ if (r)
+ goto error;
+ }

- /* Good we can use this VMID */
- if (id->last_user == ring) {
- r = amdgpu_sync_fence(ring->adev, sync,
- id->first);
+ /* And remember this submission as user of the VMID */
+ r = amdgpu_sync_fence(ring->adev, &id->active, fence);
if (r)
goto error;
- }
-
- /* And remember this submission as user of the VMID */
- r = amdgpu_sync_fence(ring->adev, &id->active, fence);
- if (r)
- goto error;

- list_move_tail(&id->list, &adev->vm_manager.ids_lru);
- vm->ids[ring->idx] = id;
+ list_move_tail(&id->list, &adev->vm_manager.ids_lru);
+ vm->ids[ring->idx] = id;

- *vm_id = id - adev->vm_manager.ids;
- *vm_pd_addr = AMDGPU_VM_NO_FLUSH;
- trace_amdgpu_vm_grab_id(vm, ring->idx, *vm_id, *vm_pd_addr);
+ *vm_id = id - adev->vm_manager.ids;
+ *vm_pd_addr = AMDGPU_VM_NO_FLUSH;
+ trace_amdgpu_vm_grab_id(vm, ring->idx, *vm_id,
+ *vm_pd_addr);

- mutex_unlock(&adev->vm_manager.lock);
- return 0;
+ mutex_unlock(&adev->vm_manager.lock);
+ return 0;

- } while (i != ring->idx);
+ } while (i != ring->idx);

- /* Check if we have an idle VMID */
- list_for_each_entry(id, &adev->vm_manager.ids_lru, list) {
- if (amdgpu_sync_is_idle(&id->active, ring))
- break;
-
- }
-
- /* If we can't find a idle VMID to use, just wait for the oldest */
- if (&id->list == &adev->vm_manager.ids_lru) {
- id = list_first_entry(&adev->vm_manager.ids_lru,
- struct amdgpu_vm_id,
- list);
+ /* Still no ID to use? Then use the idle one found earlier */
+ id = idle;
}

r = amdgpu_sync_cycle_fences(sync, &id->active, fence);
--
2.5.0
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