[libcamera-devel] [PATCH v9 06/18] libcamera: pipeline: simple: Don't rely on bufferCount

[Jacopo Mondi]

Hi Paul

On Fri, Dec 16, 2022 at 09:29:27PM +0900, Paul Elder via libcamera-devel wrote:
> From: Nícolas F. R. A. Prado <nfraprado at collabora.com>
>
> Currently the simple pipeline handler relies on bufferCount to decide on
> the number of buffers to allocate internally when a converter is in use
> and for the number of V4L2 buffer slots to reserve. Instead, the number
> of internal buffers should be the minimum required by the pipeline to
> keep the requests flowing, in order to avoid wasting memory, while the
> number of V4L2 buffer slots should be greater than the expected number
> of requests queued by the application, in order to avoid thrashing
> dmabuf mappings, which would degrade performance.
>
> Stop relying on bufferCount for these numbers and instead set them to
> appropriate, and independent, constants.
>
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado at collabora.com>
> Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>
> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
>
> ---
> Changes in v9:
> - rebased
>
> Changes in v8:
> - New
> ---
>  include/libcamera/internal/converter.h        |  3 ++-
>  .../internal/converter/converter_v4l2_m2m.h   |  6 +++--
>  .../converter/converter_v4l2_m2m.cpp          | 12 +++++-----
>  src/libcamera/pipeline/simple/simple.cpp      | 22 ++++++++++++++-----
>  4 files changed, 30 insertions(+), 13 deletions(-)
>
> diff --git a/include/libcamera/internal/converter.h b/include/libcamera/internal/converter.h
> index 834ec5ab..32490fe0 100644
> --- a/include/libcamera/internal/converter.h
> +++ b/include/libcamera/internal/converter.h
> @@ -49,7 +49,8 @@ public:
>  	virtual int exportBuffers(unsigned int output, unsigned int count,
>  				  std::vector<std::unique_ptr<FrameBuffer>> *buffers) = 0;
>
> -	virtual int start() = 0;
> +	virtual int start(unsigned int internalBufferCount,
> +			  unsigned int bufferSlotCount) = 0;
>  	virtual void stop() = 0;
>
>  	virtual int queueBuffers(FrameBuffer *input,
> diff --git a/include/libcamera/internal/converter/converter_v4l2_m2m.h b/include/libcamera/internal/converter/converter_v4l2_m2m.h
> index 815916d0..1f471071 100644
> --- a/include/libcamera/internal/converter/converter_v4l2_m2m.h
> +++ b/include/libcamera/internal/converter/converter_v4l2_m2m.h
> @@ -50,7 +50,8 @@ public:
>  	int exportBuffers(unsigned int ouput, unsigned int count,
>  			  std::vector<std::unique_ptr<FrameBuffer>> *buffers);
>
> -	int start();
> +	int start(unsigned int internalBufferCount,
> +		  unsigned int bufferSlotCount);
>  	void stop();
>
>  	int queueBuffers(FrameBuffer *input,
> @@ -69,7 +70,8 @@ private:
>  		int exportBuffers(unsigned int count,
>  				  std::vector<std::unique_ptr<FrameBuffer>> *buffers);
>
> -		int start();
> +		int start(unsigned int internalBufferCount,
> +			  unsigned int bufferSlotCount);
>  		void stop();
>
>  		int queueBuffers(FrameBuffer *input, FrameBuffer *output);
> diff --git a/src/libcamera/converter/converter_v4l2_m2m.cpp b/src/libcamera/converter/converter_v4l2_m2m.cpp
> index 2a4d1d99..9d25f25a 100644
> --- a/src/libcamera/converter/converter_v4l2_m2m.cpp
> +++ b/src/libcamera/converter/converter_v4l2_m2m.cpp
> @@ -107,13 +107,14 @@ int V4L2M2MConverter::Stream::exportBuffers(unsigned int count,
>  	return m2m_->capture()->exportBuffers(count, buffers);
>  }
>
> -int V4L2M2MConverter::Stream::start()
> +int V4L2M2MConverter::Stream::start(unsigned int internalBufferCount,
> +				    unsigned int bufferSlotCount)
>  {
> -	int ret = m2m_->output()->importBuffers(inputBufferCount_);
> +	int ret = m2m_->output()->importBuffers(internalBufferCount);
>  	if (ret < 0)
>  		return ret;
>
> -	ret = m2m_->capture()->importBuffers(outputBufferCount_);
> +	ret = m2m_->capture()->importBuffers(bufferSlotCount);

Are inputBufferCount_ and outputBufferCount_ used anymore ?
And to be honest I would keep the names as they are

Also the number of output buffers could be defined by the converter
class itself ?

>  	if (ret < 0) {
>  		stop();
>  		return ret;
> @@ -373,12 +374,13 @@ int V4L2M2MConverter::exportBuffers(unsigned int output, unsigned int count,
>  /**
>   * \copydoc libcamera::Converter::start
>   */
> -int V4L2M2MConverter::start()
> +int V4L2M2MConverter::start(unsigned int internalBufferCount,
> +			    unsigned int bufferSlotCount)
>  {
>  	int ret;
>
>  	for (Stream &stream : streams_) {
> -		ret = stream.start();
> +		ret = stream.start(internalBufferCount, bufferSlotCount);
>  		if (ret < 0) {
>  			stop();
>  			return ret;
> diff --git a/src/libcamera/pipeline/simple/simple.cpp b/src/libcamera/pipeline/simple/simple.cpp
> index 6b7c6d5c..196e5252 100644
> --- a/src/libcamera/pipeline/simple/simple.cpp
> +++ b/src/libcamera/pipeline/simple/simple.cpp
> @@ -339,6 +339,7 @@ protected:
>
>  private:
>  	static constexpr unsigned int kNumInternalBuffers = 3;
> +	static constexpr unsigned int kSimpleBufferSlotCount = 16;
>
>  	struct EntityData {
>  		std::unique_ptr<V4L2VideoDevice> video;
> @@ -1232,17 +1233,27 @@ int SimplePipelineHandler::start(Camera *camera, [[maybe_unused]] const ControlL
>  		return -EBUSY;
>  	}
>
> +	/*
> +	 * Number of internal buffers that will be used to move video capture
> +	 * device frames to the converter.
> +	 *
> +	 * \todo Make this depend on the driver in use instead of being
> +	 * hardcoded. In order to not drop frames, the realtime requirements for
> +	 * each device should be checked, so it may not be as simple as just
> +	 * using the minimum number of buffers required by the driver.
> +	 */
> +	static constexpr unsigned int internalBufferCount = 3;
> +
>  	if (data->useConverter_) {
>  		/*
>  		 * When using the converter allocate a fixed number of internal
>  		 * buffers.
>  		 */
> -		ret = video->allocateBuffers(kNumInternalBuffers,
> +		ret = video->allocateBuffers(internalBufferCount,
>  					     &data->converterBuffers_);
>  	} else {
> -		/* Otherwise, prepare for using buffers from the only stream. */
> -		Stream *stream = &data->streams_[0];
> -		ret = video->importBuffers(stream->configuration().bufferCount);
> +		/* Otherwise, prepare for using buffers. */
> +		ret = video->importBuffers(kSimpleBufferSlotCount);
>  	}
>  	if (ret < 0) {
>  		releasePipeline(data);
> @@ -1258,7 +1269,8 @@ int SimplePipelineHandler::start(Camera *camera, [[maybe_unused]] const ControlL
>  	}
>
>  	if (data->useConverter_) {
> -		ret = data->converter_->start();
> +		ret = data->converter_->start(internalBufferCount,
> +					      kSimpleBufferSlotCount);
>  		if (ret < 0) {
>  			stop(camera);
>  			return ret;
> --
> 2.35.1
>