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

[Paul Elder]

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);
 	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