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

["Christian König" <christian.koenig@amd.com>]

Am 26.02.24 um 17:52 schrieb Philip Yang:
>
> 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@amd.com>
>> Cc: Alex Deucher<alexander.deucher@amd.com>
>> Cc: Felix Kuehling<felix.kuehling@amd.com>
>> Cc: Rajneesh Bhardwaj<rajneesh.bhardwaj@amd.com>
>> Signed-off-by: Shashank Sharma<shashank.sharma@amd.com>
>> ---
>>   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,
>

The problem is that we attach the TLB flush fence only after that here 
is called.

But I agree that this is not the right approach, instead we should 
change the call to amdgpu_vm_pt_free_dfs in amdgpu_vm_ptes_update.

Basically put all the freed BOs into a list in the parameter structure 
and then call amdgpu_vm_pt_free_dfs() after adding the TLB flush fence.

Regards,
Christian.

> 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.
>
> 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;
>>   }
>>