Re: [PATCH 3/5] dma-buf: return only unsignaled fences in dma_fence_unwrap_for_each

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, May 04, 2022 at 02:22:54PM +0200, Christian König wrote:
> dma_fence_chain containers cleanup signaled fences automatically, so
> filter those out from arrays as well.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/dma-fence-unwrap.c | 23 ++++++++++++++++-------
>  include/linux/dma-fence-unwrap.h   |  4 ++--
>  2 files changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
> index 711be125428c..7b0b91086ded 100644
> --- a/drivers/dma-buf/dma-fence-unwrap.c
> +++ b/drivers/dma-buf/dma-fence-unwrap.c
> @@ -32,8 +32,13 @@ __dma_fence_unwrap_array(struct dma_fence_unwrap *cursor)
>  struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head,
>  					 struct dma_fence_unwrap *cursor)
>  {
> +	struct dma_fence *tmp;
> +
>  	cursor->chain = dma_fence_get(head);
> -	return __dma_fence_unwrap_array(cursor);
> +	tmp = __dma_fence_unwrap_array(cursor);
> +	if (tmp && dma_fence_is_signaled(tmp))
> +		tmp = dma_fence_unwrap_next(cursor);
> +	return tmp;
>  }
>  EXPORT_SYMBOL_GPL(dma_fence_unwrap_first);
>  
> @@ -48,12 +53,16 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
>  {
>  	struct dma_fence *tmp;
>  
> -	++cursor->index;
> -	tmp = dma_fence_array_next(cursor->array, cursor->index);
> -	if (tmp)
> -		return tmp;
> +	do {
> +		++cursor->index;
> +		tmp = dma_fence_array_next(cursor->array, cursor->index);
> +		if (tmp && !dma_fence_is_signaled(tmp))
> +			return tmp;

Don't do need a do {} while here too to first walk through the array
before going to the next one in the chain? Maybe add a testcase for this?

> +
> +		cursor->chain = dma_fence_chain_walk(cursor->chain);
> +		tmp = __dma_fence_unwrap_array(cursor);
> +	} while (tmp && dma_fence_is_signaled(tmp));
>  
> -	cursor->chain = dma_fence_chain_walk(cursor->chain);
> -	return __dma_fence_unwrap_array(cursor);
> +	return tmp;
>  }
>  EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
> diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
> index e7c219da4ed7..e9d114637294 100644
> --- a/include/linux/dma-fence-unwrap.h
> +++ b/include/linux/dma-fence-unwrap.h
> @@ -41,8 +41,8 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);
>   * @head: starting point for the iterator
>   *
>   * Unwrap dma_fence_chain and dma_fence_array containers and deep dive into all
> - * potential fences in them. If @head is just a normal fence only that one is
> - * returned.
> + * potential none signaled fences in them. If @head is just a normal fence only
> + * that one is returned.

I think I get what you want to say, but it reads garbled. What about
leaving the current text as-is and adding something like

"Note that signalled fences are opportunistically filtered out, which
means the iteration is potentially over no fence at all"

Or something like that? I think smashing this all into one sentence
doesn't work well.

Then please also add this same sentence to unwrap_first/next() for
completeness.
-Daniel

>   */
>  #define dma_fence_unwrap_for_each(fence, cursor, head)			\
>  	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch