[libcamera-devel] [PATCH 3/3] cam: Drop frames once the capture limit is reached

[Kieran Bingham]

Quoting Laurent Pinchart (2021-10-12 03:23:21)
> The camera session keeps requeuing requests until the capture limit is
> reached. This causes more request than the limit to complete, as there's
> a queue of requests in flight. When capturing from multiple cameras
> concurrently, this results in the captureDone signal being emitted for
> every request completion after the limit is reached, instead of once per
> camera session when reaching the limit.
> 
> Fix this by simply dropping any request that completes after the limit
> is reached. We could instead avoid requeuing more requests than needed
> to reach the limit, but that may cause request starvation in pipelines,
> which are currently not handled consistently (or correctly).
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/cam/camera_session.cpp | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/src/cam/camera_session.cpp b/src/cam/camera_session.cpp
> index 605018278c5a..594cd51bb6a2 100644
> --- a/src/cam/camera_session.cpp
> +++ b/src/cam/camera_session.cpp
> @@ -348,6 +348,9 @@ void CameraSession::processRequest(Request *request)
>  {
>         const Request::BufferMap &buffers = request->buffers();
>  

I'd be tempted to put a comment here to explain that this is different
from, and required as well as the similar check down at the end of the
function.

But either way:


Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> +       if (captureLimit_ && captureCount_ >= captureLimit_)
> +               return;
> +
>         /*
>          * Compute the frame rate. The timestamp is arbitrarily retrieved from
>          * the first buffer, as all buffers should have matching timestamps.
> -- 
> Regards,
> 
> Laurent Pinchart
>