Re: [PATCH v3 3/3] drm/amdgpu: sync page table freeing with tlb flush

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On 26/02/2024 17:52, Philip Yang wrote:


On 2024-02-23 08:42, Shashank Sharma wrote:
This patch:
- adds a new list in amdgou_vm to hold the VM PT entries being freed
- waits for the TLB flush using the vm->tlb_flush_fence
- actually frees the PT BOs

V2: rebase
V3: Do not attach the tlb_fence to the entries, rather add the entries
     to a list and delay their freeing (Christian)

Cc: Christian König<Christian.Koenig@xxxxxxx>
Cc: Alex Deucher<alexander.deucher@xxxxxxx>
Cc: Felix Kuehling<felix.kuehling@xxxxxxx>
Cc: Rajneesh Bhardwaj<rajneesh.bhardwaj@xxxxxxx>
Signed-off-by: Shashank Sharma<shashank.sharma@xxxxxxx>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c    |  6 +++
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h    |  6 +++
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 51 ++++++++++++++++++++---
  3 files changed, 58 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index 67c690044b97..eebb73f2c2ef 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -939,6 +939,10 @@ int amdgpu_vm_update_range(struct amdgpu_device *adev, struct amdgpu_vm *vm,
  		/* Makes sure no PD/PT is freed before the flush */
  		dma_resv_add_fence(vm->root.bo->tbo.base.resv, *fence,
  				   DMA_RESV_USAGE_BOOKKEEP);
+
+		mutex_lock(&vm->tlb_fence_lock);
+		vm->tlb_fence_last = *fence;
+		mutex_unlock(&vm->tlb_fence_lock);
  	}
amdgpu_res_first(pages_addr ? NULL : res, offset,
@@ -2212,6 +2216,7 @@ int amdgpu_vm_init(struct amdgpu_device *adev, struct amdgpu_vm *vm,
  	INIT_LIST_HEAD(&vm->freed);
  	INIT_LIST_HEAD(&vm->done);
  	INIT_LIST_HEAD(&vm->pt_freed);
+	INIT_LIST_HEAD(&vm->tlb_flush_waitlist);
  	INIT_WORK(&vm->pt_free_work, amdgpu_vm_pt_free_work);
  	INIT_KFIFO(vm->faults);
@@ -2244,6 +2249,7 @@ int amdgpu_vm_init(struct amdgpu_device *adev, struct amdgpu_vm *vm,
  	vm->last_unlocked = dma_fence_get_stub();
  	vm->generation = 0;
+ mutex_init(&vm->tlb_fence_lock);
  	mutex_init(&vm->eviction_lock);
  	vm->evicting = false;
  	vm->tlb_fence_context = dma_fence_context_alloc(1);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
index 8e6fd25d07b7..77f10ed80973 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
@@ -334,6 +334,10 @@ struct amdgpu_vm {
  	uint64_t		*tlb_seq_cpu_addr;
  	uint64_t		tlb_fence_context;
+ struct mutex tlb_fence_lock;
+	struct dma_fence	*tlb_fence_last;
+	struct list_head	tlb_flush_waitlist;
+
  	atomic64_t		kfd_last_flushed_seq;
/* How many times we had to re-generate the page tables */
@@ -379,6 +383,8 @@ struct amdgpu_vm {
/* cached fault info */
  	struct amdgpu_vm_fault_info fault_info;
+
+	int count_bos;
  };
struct amdgpu_vm_manager {
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
index 95dc0afdaffb..57ea95c5c085 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
@@ -643,13 +643,13 @@ static void amdgpu_vm_pt_free(struct amdgpu_vm_bo_base *entry)
  	if (!entry->bo)
  		return;
- entry->bo->vm_bo = NULL;
  	shadow = amdgpu_bo_shadowed(entry->bo);
  	if (shadow) {
  		ttm_bo_set_bulk_move(&shadow->tbo, NULL);
  		amdgpu_bo_unref(&shadow);
  	}
  	ttm_bo_set_bulk_move(&entry->bo->tbo, NULL);
+	entry->bo->vm_bo = NULL;
spin_lock(&entry->vm->status_lock);
  	list_del(&entry->vm_status);
@@ -657,6 +657,38 @@ static void amdgpu_vm_pt_free(struct amdgpu_vm_bo_base *entry)
  	amdgpu_bo_unref(&entry->bo);
  }
+static void amdgpu_vm_pt_flush_waitlist(struct amdgpu_vm *vm)
+{
+	struct amdgpu_vm_bo_base *entry, *next;
+	LIST_HEAD(tlb_flush_waitlist);
+
+	if (!vm || list_empty(&vm->tlb_flush_waitlist))
+		return;
+
+	/* Wait for pending TLB flush before freeing PT BOs */
+	mutex_lock(&vm->tlb_fence_lock);
+	if (vm->tlb_fence_last && !dma_fence_is_signaled(vm->tlb_fence_last)) {
+		if (dma_fence_wait_timeout(vm->tlb_fence_last, false,
+					   MAX_SCHEDULE_TIMEOUT) <= 0) {
+			DRM_ERROR("Timedout waiting for TLB flush, not freeing PT BOs\n");
+			mutex_unlock(&vm->tlb_fence_lock);
+			return;
+		}
+
+		vm->tlb_fence_last = NULL;
+	}
+
+	/* Save the waitlist locally and reset the flushlist */
+	list_splice_init(&vm->tlb_flush_waitlist, &tlb_flush_waitlist);
+	mutex_unlock(&vm->tlb_fence_lock);
+
+	/* Now free the entries */
+	list_for_each_entry_safe(entry, next, &tlb_flush_waitlist, vm_status) {
+		if (entry)
+			amdgpu_vm_pt_free(entry);
+	}
+}
+
  void amdgpu_vm_pt_free_work(struct work_struct *work)
  {
  	struct amdgpu_vm_bo_base *entry, *next;
@@ -673,7 +705,7 @@ void amdgpu_vm_pt_free_work(struct work_struct *work)
  	amdgpu_bo_reserve(vm->root.bo, true);
list_for_each_entry_safe(entry, next, &pt_freed, vm_status)
-		amdgpu_vm_pt_free(entry);
+		list_move(&entry->vm_status, &vm->tlb_flush_waitlist);
amdgpu_bo_unreserve(vm->root.bo);
  }
@@ -708,11 +740,17 @@ static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
  		return;
  	}
- for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
-		amdgpu_vm_pt_free(entry);
+	mutex_lock(&vm->tlb_fence_lock);
+
+	for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry) {
+		if (entry)
+			list_add(&entry->vm_status, &vm->tlb_flush_waitlist);
+	}
if (start)
-		amdgpu_vm_pt_free(start->entry);
+		list_add(&start->entry->vm_status, &vm->tlb_flush_waitlist);
+
+	mutex_unlock(&vm->tlb_fence_lock);

Because pt bo attached with tlb flush fence already, so amdgpu_vm_pt_free will not free the bo, the tlb flush work will signal the tlb fence, and then the pt bo will be freed.

To add freed pt bo to vm->tlb_flush_waitlist, and then wait for tlb flush fence at end of updating mapping is unnecessary, this patch seems redundant.

Thanks for the review Philip, I guess the problem was due to the placement of attachment of pt_bo with fence, which I will move to the end (in patch 2), which will make this patch valid again.

- Shashank

Regards,

Philip

  }
/**
@@ -725,6 +763,7 @@ static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
  void amdgpu_vm_pt_free_root(struct amdgpu_device *adev, struct amdgpu_vm *vm)
  {
  	amdgpu_vm_pt_free_dfs(adev, vm, NULL, false);
+	amdgpu_vm_pt_flush_waitlist(vm);
  }
/**
@@ -1070,6 +1109,8 @@ int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
  		}
  	}
+ /* Actually free the buffers now */
+	amdgpu_vm_pt_flush_waitlist(params->vm);
  	return 0;
  }



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