[libcamera-devel] [PATCH 3/3] pipeline: raspberrypi: Increase the V4L2BufferCache slot allocations

[Kieran Bingham]

Quoting Naushir Patuck (2021-11-10 10:08:02)
> If a stream is marked as external, double the number of V4L2BufferCache slots
> that are allocated. This is to account for additional buffers that may be
> allocated directly by the application.
> 
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> ---
>  src/libcamera/pipeline/raspberrypi/rpi_stream.cpp | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp b/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp
> index b3265d0e8aab..67901936d6b6 100644
> --- a/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp
> +++ b/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp
> @@ -107,6 +107,14 @@ int Stream::prepareBuffers(unsigned int count)
>                 count = bufferMap_.size();
>         }
>  
> +       /*
> +        * If this is an external stream, we must allocate slots for buffers that
> +        * might be externally allocated. We have no indication of how many buffers
> +        * may be used, so this might overallocate slots in the buffer cache.
> +        */

Perhaps we'll need a better system here (not in this patch) to handle
this ... but I think overallocating is cheap - and the whole point of
the buffer cache is to try to re-use the same buffers where possible. So
I /think/ overallocations is the right solution for now anyway.

> +       if (isExternal())
> +               count = count * 2;

Of course it's hard to know /how/ far to overallocate ... But this will
do until we figure it out ;-)


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

> +
>         return dev_->importBuffers(count);
>  }
>  
> -- 
> 2.25.1
>