linux-kernel - Re: [PATCH v14 53/56] media: core: Free range of buffers

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Message-ID: <20231109091018.tzodchqp44tmwq3k@chromium.org>
Date:   Thu, 9 Nov 2023 09:10:18 +0000
From:   Tomasz Figa <tfiga@...omium.org>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     mchehab@...nel.org, m.szyprowski@...sung.com, ming.qian@....com,
        ezequiel@...guardiasur.com.ar, p.zabel@...gutronix.de,
        gregkh@...uxfoundation.org, hverkuil-cisco@...all.nl,
        nicolas.dufresne@...labora.com, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
        kernel@...labora.com
Subject: Re: [PATCH v14 53/56] media: core: Free range of buffers

On Tue, Oct 31, 2023 at 05:31:01PM +0100, Benjamin Gaignard wrote:
> Improve __vb2_queue_free() and __vb2_free_mem() to free
> range of buffers and not only the last few buffers.
> Intoduce starting index to be flexible on range and change the loops
> according to this parameters.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> ---
>  .../media/common/videobuf2/videobuf2-core.c   | 59 +++++++++----------
>  1 file changed, 28 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index 6e88406fcae9..010a8bca0240 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -519,15 +519,13 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>  /*
>   * __vb2_free_mem() - release all video buffer memory for a given queue

This comment is kind of outdated. Maybe we should replace it with

	release video buffer memory for a given range of buffers in a given
	queue

?

>   */
> -static void __vb2_free_mem(struct vb2_queue *q, unsigned int buffers)
> +static void __vb2_free_mem(struct vb2_queue *q, unsigned int start, unsigned int count)
>  {
> -	unsigned int buffer;
> +	unsigned int i;
>  	struct vb2_buffer *vb;
> -	unsigned int q_num_buffers = vb2_get_num_buffers(q);
>  
> -	for (buffer = q_num_buffers - buffers; buffer < q_num_buffers;
> -	     ++buffer) {
> -		vb = vb2_get_buffer(q, buffer);
> +	for (i = start; i < q->max_num_buffers && i < start + count; i++) {

We could make this (and all those numerous simialr iterations) more
efficient by using bitmap helpers (probably wrapped in some vb2 helpers),
e.g. for_each_set_bit_from() (vb2_for_each_buffer_from()?). It can be done
in a follow up patch separately from this series though.

> +		vb = vb2_get_buffer(q, i);
>  		if (!vb)
>  			continue;
>  
> @@ -542,35 +540,35 @@ static void __vb2_free_mem(struct vb2_queue *q, unsigned int buffers)
>  }
>  
>  /*
> - * __vb2_queue_free() - free buffers at the end of the queue - video memory and
> + * __vb2_queue_free() - free count buffers from start index of the queue - video memory and

nit: How about using the @count and @start notation to refer the argument
names? (Can be done with a follow up patch outside of this series later.)

>   * related information, if no buffers are left return the queue to an
>   * uninitialized state. Might be called even if the queue has already been freed.
>   */
> -static void __vb2_queue_free(struct vb2_queue *q, unsigned int buffers)
> +static void __vb2_queue_free(struct vb2_queue *q, unsigned int start, unsigned int count)
>  {
> -	unsigned int buffer;
> -	unsigned int q_num_buffers = vb2_get_num_buffers(q);
> +	unsigned int i;
>  
>  	lockdep_assert_held(&q->mmap_lock);
>  
>  	/* Call driver-provided cleanup function for each buffer, if provided */
> -	for (buffer = q_num_buffers - buffers; buffer < q_num_buffers;
> -	     ++buffer) {
> -		struct vb2_buffer *vb = vb2_get_buffer(q, buffer);
> +	for (i = start; i < q->max_num_buffers && i < start + count; i++) {
> +		struct vb2_buffer *vb = vb2_get_buffer(q, i);
>  
> -		if (vb && vb->planes[0].mem_priv)
> +		if (!vb)
> +			continue;
> +		if (vb->planes[0].mem_priv)

nit: Not sure if we really had to change this, but I'm fine with either.

Best regards,
Tomasz