[v4,6/6] libcamera: software_isp: Run sw-statistics once every 4th frame

24539 diff mbox series

Run sw-statistics once every 4th frame, instead of every frame. There are
2 reasons for this:

1. There really is no need to have statistics for every frame and only
doing this every 4th frame helps save some CPU time.

2. The generic nature of the simple pipeline-handler, so no information
about possible CSI receiver frame-delays. In combination with the software
ISP often being used with sensors without sensor info in the sensor-helper
code, so no reliable control-delay information means that the software ISP
is prone to AGC oscillation. Skipping statistics gathering also means
skipping running the AGC algorithm slowing it down, avoiding this
oscillation.

Note ideally the AGC oscillation problem would be fixed by adding sensor
metadata support all through the stack so that the exact gain and exposure
used for a specific frame are reliably provided by the sensor metadata.

Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Milan Zamazal <mzamazal@redhat.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Hans de Goede <hansg@kernel.org>
---
Changes in v4:
- Document why to skip 3 frames / why once every 4 frames
- Pass frame number to SwStatsCpu::startFrame() SwStatsCpu::processLine?()
  and move all skipping handling to inside the SwStatsCpu class
---
 src/libcamera/software_isp/debayer_cpu.cpp | 18 +++++++++---------
 src/libcamera/software_isp/debayer_cpu.h   |  4 ++--
 src/libcamera/software_isp/swstats_cpu.cpp | 19 +++++++++++++++----
 src/libcamera/software_isp/swstats_cpu.h   | 20 +++++++++++++++++---
 4 files changed, 43 insertions(+), 18 deletions(-)

Hans de Goede <hansg@kernel.org> writes:

> Run sw-statistics once every 4th frame, instead of every frame. There are
> 2 reasons for this:
>
> 1. There really is no need to have statistics for every frame and only
> doing this every 4th frame helps save some CPU time.
>
> 2. The generic nature of the simple pipeline-handler, so no information
> about possible CSI receiver frame-delays. In combination with the software
> ISP often being used with sensors without sensor info in the sensor-helper
> code, so no reliable control-delay information means that the software ISP
> is prone to AGC oscillation. Skipping statistics gathering also means
> skipping running the AGC algorithm slowing it down, avoiding this
> oscillation.
>
> Note ideally the AGC oscillation problem would be fixed by adding sensor
> metadata support all through the stack so that the exact gain and exposure
> used for a specific frame are reliably provided by the sensor metadata.
>
> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> Tested-by: Milan Zamazal <mzamazal@redhat.com>
> Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> Signed-off-by: Hans de Goede <hansg@kernel.org>

I'm still not excited about `frame % kStatPerNumFrames' spread in
multiple places but I can live with it.

Reviewed-by: Milan Zamazal <mzamazal@redhat.com>

> ---
> Changes in v4:
> - Document why to skip 3 frames / why once every 4 frames
> - Pass frame number to SwStatsCpu::startFrame() SwStatsCpu::processLine?()
>   and move all skipping handling to inside the SwStatsCpu class
> ---
>  src/libcamera/software_isp/debayer_cpu.cpp | 18 +++++++++---------
>  src/libcamera/software_isp/debayer_cpu.h   |  4 ++--
>  src/libcamera/software_isp/swstats_cpu.cpp | 19 +++++++++++++++----
>  src/libcamera/software_isp/swstats_cpu.h   | 20 +++++++++++++++++---
>  4 files changed, 43 insertions(+), 18 deletions(-)
>
> diff --git a/src/libcamera/software_isp/debayer_cpu.cpp b/src/libcamera/software_isp/debayer_cpu.cpp
> index 2dc85e5e0..d5fd0ae73 100644
> --- a/src/libcamera/software_isp/debayer_cpu.cpp
> +++ b/src/libcamera/software_isp/debayer_cpu.cpp
> @@ -655,7 +655,7 @@ void DebayerCpu::memcpyNextLine(const uint8_t *linePointers[])
>  	lineBufferIndex_ = (lineBufferIndex_ + 1) % (patternHeight + 1);
>  }
>  
> -void DebayerCpu::process2(const uint8_t *src, uint8_t *dst)
> +void DebayerCpu::process2(uint32_t frame, const uint8_t *src, uint8_t *dst)
>  {
>  	unsigned int yEnd = window_.y + window_.height;
>  	/* Holds [0] previous- [1] current- [2] next-line */
> @@ -681,7 +681,7 @@ void DebayerCpu::process2(const uint8_t *src, uint8_t *dst)
>  	for (unsigned int y = window_.y; y < yEnd; y += 2) {
>  		shiftLinePointers(linePointers, src);
>  		memcpyNextLine(linePointers);
> -		stats_->processLine0(y, linePointers);
> +		stats_->processLine0(frame, y, linePointers);
>  		(this->*debayer0_)(dst, linePointers);
>  		src += inputConfig_.stride;
>  		dst += outputConfig_.stride;
> @@ -696,7 +696,7 @@ void DebayerCpu::process2(const uint8_t *src, uint8_t *dst)
>  	if (window_.y == 0) {
>  		shiftLinePointers(linePointers, src);
>  		memcpyNextLine(linePointers);
> -		stats_->processLine0(yEnd, linePointers);
> +		stats_->processLine0(frame, yEnd, linePointers);
>  		(this->*debayer0_)(dst, linePointers);
>  		src += inputConfig_.stride;
>  		dst += outputConfig_.stride;
> @@ -710,7 +710,7 @@ void DebayerCpu::process2(const uint8_t *src, uint8_t *dst)
>  	}
>  }
>  
> -void DebayerCpu::process4(const uint8_t *src, uint8_t *dst)
> +void DebayerCpu::process4(uint32_t frame, const uint8_t *src, uint8_t *dst)
>  {
>  	const unsigned int yEnd = window_.y + window_.height;
>  	/*
> @@ -733,7 +733,7 @@ void DebayerCpu::process4(const uint8_t *src, uint8_t *dst)
>  	for (unsigned int y = window_.y; y < yEnd; y += 4) {
>  		shiftLinePointers(linePointers, src);
>  		memcpyNextLine(linePointers);
> -		stats_->processLine0(y, linePointers);
> +		stats_->processLine0(frame, y, linePointers);
>  		(this->*debayer0_)(dst, linePointers);
>  		src += inputConfig_.stride;
>  		dst += outputConfig_.stride;
> @@ -746,7 +746,7 @@ void DebayerCpu::process4(const uint8_t *src, uint8_t *dst)
>  
>  		shiftLinePointers(linePointers, src);
>  		memcpyNextLine(linePointers);
> -		stats_->processLine2(y, linePointers);
> +		stats_->processLine2(frame, y, linePointers);
>  		(this->*debayer2_)(dst, linePointers);
>  		src += inputConfig_.stride;
>  		dst += outputConfig_.stride;
> @@ -821,12 +821,12 @@ void DebayerCpu::process(uint32_t frame, FrameBuffer *input, FrameBuffer *output
>  		return;
>  	}
>  
> -	stats_->startFrame();
> +	stats_->startFrame(frame);
>  
>  	if (inputConfig_.patternSize.height == 2)
> -		process2(in.planes()[0].data(), out.planes()[0].data());
> +		process2(frame, in.planes()[0].data(), out.planes()[0].data());
>  	else
> -		process4(in.planes()[0].data(), out.planes()[0].data());
> +		process4(frame, in.planes()[0].data(), out.planes()[0].data());
>  
>  	metadata.planes()[0].bytesused = out.planes()[0].size();
>  
> diff --git a/src/libcamera/software_isp/debayer_cpu.h b/src/libcamera/software_isp/debayer_cpu.h
> index 9d343e464..03e0d7843 100644
> --- a/src/libcamera/software_isp/debayer_cpu.h
> +++ b/src/libcamera/software_isp/debayer_cpu.h
> @@ -133,8 +133,8 @@ private:
>  	void setupInputMemcpy(const uint8_t *linePointers[]);
>  	void shiftLinePointers(const uint8_t *linePointers[], const uint8_t *src);
>  	void memcpyNextLine(const uint8_t *linePointers[]);
> -	void process2(const uint8_t *src, uint8_t *dst);
> -	void process4(const uint8_t *src, uint8_t *dst);
> +	void process2(uint32_t frame, const uint8_t *src, uint8_t *dst);
> +	void process4(uint32_t frame, const uint8_t *src, uint8_t *dst);
>  
>  	/* Max. supported Bayer pattern height is 4, debayering this requires 5 lines */
>  	static constexpr unsigned int kMaxLineBuffers = 5;
> diff --git a/src/libcamera/software_isp/swstats_cpu.cpp b/src/libcamera/software_isp/swstats_cpu.cpp
> index eb416dfdc..634ebfc3c 100644
> --- a/src/libcamera/software_isp/swstats_cpu.cpp
> +++ b/src/libcamera/software_isp/swstats_cpu.cpp
> @@ -62,8 +62,9 @@ namespace libcamera {
>   */
>  
>  /**
> - * \fn void SwStatsCpu::processLine0(unsigned int y, const uint8_t *src[])
> + * \fn void SwStatsCpu::processLine0(uint32_t frame, unsigned int y, const uint8_t *src[])
>   * \brief Process line 0
> + * \param[in] frame The frame number
>   * \param[in] y The y coordinate.
>   * \param[in] src The input data.
>   *
> @@ -74,8 +75,9 @@ namespace libcamera {
>   */
>  
>  /**
> - * \fn void SwStatsCpu::processLine2(unsigned int y, const uint8_t *src[])
> + * \fn void SwStatsCpu::processLine2(uint32_t frame, unsigned int y, const uint8_t *src[])
>   * \brief Process line 2 and 3
> + * \param[in] frame The frame number
>   * \param[in] y The y coordinate.
>   * \param[in] src The input data.
>   *
> @@ -89,6 +91,11 @@ namespace libcamera {
>   * \brief Signals that the statistics are ready
>   */
>  
> +/**
> + * \var SwStatsCpu::kStatPerNumFrames
> + * \brief Run stats once every kStatPerNumFrames frames
> + */
> +
>  /**
>   * \typedef SwStatsCpu::statsProcessFn
>   * \brief Called when there is data to get statistics from
> @@ -295,11 +302,15 @@ void SwStatsCpu::statsGBRG10PLine0(const uint8_t *src[])
>  
>  /**
>   * \brief Reset state to start statistics gathering for a new frame
> + * \param[in] frame The frame number
>   *
>   * This may only be called after a successful setWindow() call.
>   */
> -void SwStatsCpu::startFrame(void)
> +void SwStatsCpu::startFrame(uint32_t frame)
>  {
> +	if (frame % kStatPerNumFrames)
> +		return;
> +
>  	if (window_.width == 0)
>  		LOG(SwStatsCpu, Error) << "Calling startFrame() without setWindow()";
>  
> @@ -318,7 +329,7 @@ void SwStatsCpu::startFrame(void)
>   */
>  void SwStatsCpu::finishFrame(uint32_t frame, uint32_t bufferId)
>  {
> -	stats_.valid = true;
> +	stats_.valid = frame % kStatPerNumFrames == 0;
>  	*sharedStats_ = stats_;
>  	statsReady.emit(frame, bufferId);
>  }
> diff --git a/src/libcamera/software_isp/swstats_cpu.h b/src/libcamera/software_isp/swstats_cpu.h
> index 26a2f462e..fae575f85 100644
> --- a/src/libcamera/software_isp/swstats_cpu.h
> +++ b/src/libcamera/software_isp/swstats_cpu.h
> @@ -32,6 +32,14 @@ public:
>  	SwStatsCpu();
>  	~SwStatsCpu() = default;
>  
> +	/*
> +	 * The combination of pipeline + sensor delays means that
> +	 * exposure changes can take up to 3 frames to get applied,
> +	 * Run stats once every 4 frames to ensure any previous
> +	 * exposure changes have been applied.
> +	 */
> +	static constexpr uint32_t kStatPerNumFrames = 4;
> +
>  	bool isValid() const { return sharedStats_.fd().isValid(); }
>  
>  	const SharedFD &getStatsFD() { return sharedStats_.fd(); }
> @@ -40,11 +48,14 @@ public:
>  
>  	int configure(const StreamConfiguration &inputCfg);
>  	void setWindow(const Rectangle &window);
> -	void startFrame();
> +	void startFrame(uint32_t frame);
>  	void finishFrame(uint32_t frame, uint32_t bufferId);
>  
> -	void processLine0(unsigned int y, const uint8_t *src[])
> +	void processLine0(uint32_t frame, unsigned int y, const uint8_t *src[])
>  	{
> +		if (frame % kStatPerNumFrames)
> +			return;
> +
>  		if ((y & ySkipMask_) || y < static_cast<unsigned int>(window_.y) ||
>  		    y >= (window_.y + window_.height))
>  			return;
> @@ -52,8 +63,11 @@ public:
>  		(this->*stats0_)(src);
>  	}
>  
> -	void processLine2(unsigned int y, const uint8_t *src[])
> +	void processLine2(uint32_t frame, unsigned int y, const uint8_t *src[])
>  	{
> +		if (frame % kStatPerNumFrames)
> +			return;
> +
>  		if ((y & ySkipMask_) || y < static_cast<unsigned int>(window_.y) ||
>  		    y >= (window_.y + window_.height))
>  			return;