[PATCH] dma-buf: keep the signaling time of merged fences v3

[Luben Tuikov]

On 2023-06-30 08:00, Christian König wrote:
> Some Android CTS is testing if the signaling time keeps consistent
> during merges.
> 
> v2: use the current time if the fence is still in the signaling path and
> the timestamp not yet available.
> v3: improve comment, fix one more case to use the correct timestamp
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>  drivers/dma-buf/dma-fence-unwrap.c | 26 ++++++++++++++++++++++----
>  drivers/dma-buf/dma-fence.c        |  5 +++--
>  drivers/gpu/drm/drm_syncobj.c      |  2 +-
>  include/linux/dma-fence.h          |  2 +-
>  4 files changed, 27 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
> index 7002bca792ff..c625bb2b5d56 100644
> --- a/drivers/dma-buf/dma-fence-unwrap.c
> +++ b/drivers/dma-buf/dma-fence-unwrap.c
> @@ -66,18 +66,36 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
>  {
>  	struct dma_fence_array *result;
>  	struct dma_fence *tmp, **array;
> +	ktime_t timestamp;
>  	unsigned int i;
>  	size_t count;
>  
>  	count = 0;
> +	timestamp = ns_to_ktime(0);
>  	for (i = 0; i < num_fences; ++i) {
> -		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i])
> -			if (!dma_fence_is_signaled(tmp))
> +		dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) {
> +			if (!dma_fence_is_signaled(tmp)) {
>  				++count;
> +			} else if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT,
> +					    &tmp->flags)) {
> +				if (ktime_after(tmp->timestamp, timestamp))
> +					timestamp = tmp->timestamp;
> +			} else {
> +				/*
> +				 * Use the current time if the fence is
> +				 * currently signaling.
> +				 */
> +				timestamp = ktime_get();
> +			}
> +		}
>  	}
>  
> +	/*
> +	 * If we couldn't find a pending fence just return a private signaled
> +	 * fence with the timestamp of the last signaled one.
> +	 */
>  	if (count == 0)
> -		return dma_fence_get_stub();
> +		return dma_fence_allocate_private_stub(timestamp);
>  

Hi Christian,

Thank you for clarifying the justification of this patch in the patch description,
and adding the comment before "if (count == 0)"--it's clearer now.

Reviewed-by: Luben Tuikov <luben.tuikov at amd.com>

Thanks again for sending a v3 of this patch--it does make it clearer now. Feel
free to push this patch in.

---
Silly question perhaps:
	Could we not have returned an existing (signalled) fence with
the wanted timestamp (when count == 0), as opposed to allocating a stub? Maybe
allocation should be avoided?
-- 
Regards,
Luben

>  	array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
>  	if (!array)
> @@ -138,7 +156,7 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
>  	} while (tmp);
>  
>  	if (count == 0) {
> -		tmp = dma_fence_get_stub();
> +		tmp = dma_fence_allocate_private_stub(ktime_get());
>  		goto return_tmp;
>  	}
>  
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index f177c56269bb..ad076f208760 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -150,10 +150,11 @@ EXPORT_SYMBOL(dma_fence_get_stub);
>  
>  /**
>   * dma_fence_allocate_private_stub - return a private, signaled fence
> + * @timestamp: timestamp when the fence was signaled
>   *
>   * Return a newly allocated and signaled stub fence.
>   */
> -struct dma_fence *dma_fence_allocate_private_stub(void)
> +struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp)
>  {
>  	struct dma_fence *fence;
>  
> @@ -169,7 +170,7 @@ struct dma_fence *dma_fence_allocate_private_stub(void)
>  	set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
>  		&fence->flags);
>  
> -	dma_fence_signal(fence);
> +	dma_fence_signal_timestamp(fence, timestamp);
>  
>  	return fence;
>  }
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 0c2be8360525..04589a35eb09 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -353,7 +353,7 @@ EXPORT_SYMBOL(drm_syncobj_replace_fence);
>   */
>  static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
>  {
> -	struct dma_fence *fence = dma_fence_allocate_private_stub();
> +	struct dma_fence *fence = dma_fence_allocate_private_stub(ktime_get());
>  
>  	if (IS_ERR(fence))
>  		return PTR_ERR(fence);
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index d54b595a0fe0..0d678e9a7b24 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -606,7 +606,7 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
>  void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
>  
>  struct dma_fence *dma_fence_get_stub(void);
> -struct dma_fence *dma_fence_allocate_private_stub(void);
> +struct dma_fence *dma_fence_allocate_private_stub(ktime_t timestamp);
>  u64 dma_fence_context_alloc(unsigned num);
>  
>  extern const struct dma_fence_ops dma_fence_array_ops;