[libcamera-devel] [PATCH v9 05/18] libcamera: pipeline: ipu3: Don't rely on bufferCount

[Paul Elder]

Hi Umang,

On Wed, Dec 21, 2022 at 04:09:21PM +0530, Umang Jain wrote:
> Hi Paul,
> 
> On 12/16/22 5:59 PM, Paul Elder via libcamera-devel wrote:
> > From: Nícolas F. R. A. Prado <nfraprado at collabora.com>
> > 
> > Currently the ipu3 pipeline handler relies on bufferCount to decide on
> > the number of V4L2 buffer slots to reserve as well as for the number of
> > buffers to allocate internally for the CIO2 raw buffers and
> > parameter-statistics ImgU buffer pairs. Instead, the number of internal
> > buffers should be the minimum required by the pipeline to keep the
> > requests flowing without frame drops, in order to avoid wasting memory,
> 
> This is now sounding like the number of internal buffers should be allocated
> based on MinimumRequests property we just defined? Can it be then pivoted to
> Minimum requests property ? I don't see possibility where  internal buffers
> needed to be allocated comes out to be less than the camera's
> MinimumRequests to avoid frame drops.

Indeed I don't think there would be a situation where there would be
less internal buffers than MinimumRequests, but I think (also as is seen
throughout this series) it's possible that the number of internal
buffers could be greater than MinimumRequests.

I suppose it would be less duplication if the number of internal buffers
was defined based on MinimumRequests (eg. kIPU3BufferSlotCount =
MinimumRequests + 1). Well, not the property directly but the quantity
that is fed to the property.

> 
> > while the number of V4L2 buffer slots should be greater than the
> > expected number of requests queued by the application, in order to avoid
> 
> s/expected number of requests queued by the application/Minimum Requests
> needed to be queued by the application/
> 
> I think in this case we want a mutiplier to MinimumRequests so allocate
> larger V4L2 slots, For e.g. in context of this patch,
> 
>     kIPU3BufferSlotCount  =  4 * minimumRequests;
> 
> My goal is that, instead of defining arbitrary constants for both IMGU and
> CIO2 internal buffers , we better pivot the buffers counts to
> MinimumRequests so it would be more cleaner and logical ?  What do you
> think?

I don't think the IMGU and CIO2 internal buffers are defined off of
arbitrary constants; they're intentional constants with (documented)
rationales. But indeed I think there is benefit in defining them based
on MinimumRequests, such that they end up with the desired quantity.

> > thrashing dmabuf mappings, which would degrade performance.
> 
> Have you checked any performance metrics with increasing internal counts? 

I haven't yet. I don't have an IPU3 platform that I can test on anymore.
I'll test it on imx8mp at least.

> The comments  (and this series) overwhelming  says "without frame drops"
> throughout - but I am not sure if that's the case in reality. But the
> direction is more or less correct in my opinion.
> 
> (The feedback applies to other platforms as well, regarding pivoting
> constants the MinimumRequests property, so I rather not comment on them
> individually)


Thanks,

Paul

> > 
> > 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:
> > - rebase
> > 
> > Changes in v8:
> > - New
> > ---
> >   src/libcamera/pipeline/ipu3/cio2.cpp |  4 ++--
> >   src/libcamera/pipeline/ipu3/cio2.h   | 16 +++++++++++++++-
> >   src/libcamera/pipeline/ipu3/imgu.cpp | 12 ++++++------
> >   src/libcamera/pipeline/ipu3/imgu.h   | 15 ++++++++++++++-
> >   src/libcamera/pipeline/ipu3/ipu3.cpp | 20 ++++++++------------
> >   5 files changed, 45 insertions(+), 22 deletions(-)
> > 
> > diff --git a/src/libcamera/pipeline/ipu3/cio2.cpp b/src/libcamera/pipeline/ipu3/cio2.cpp
> > index d4e523af..feb69991 100644
> > --- a/src/libcamera/pipeline/ipu3/cio2.cpp
> > +++ b/src/libcamera/pipeline/ipu3/cio2.cpp
> > @@ -335,13 +335,13 @@ int CIO2Device::exportBuffers(unsigned int count,
> >   	return output_->exportBuffers(count, buffers);
> >   }
> > -int CIO2Device::start()
> > +int CIO2Device::start(unsigned int bufferSlotCount)
> >   {
> >   	int ret = output_->exportBuffers(kBufferCount, &buffers_);
> >   	if (ret < 0)
> >   		return ret;
> > -	ret = output_->importBuffers(kBufferCount);
> > +	ret = output_->importBuffers(bufferSlotCount);
> >   	if (ret)
> >   		LOG(IPU3, Error) << "Failed to import CIO2 buffers";
> > diff --git a/src/libcamera/pipeline/ipu3/cio2.h b/src/libcamera/pipeline/ipu3/cio2.h
> > index 68504a2d..8ed208d3 100644
> > --- a/src/libcamera/pipeline/ipu3/cio2.h
> > +++ b/src/libcamera/pipeline/ipu3/cio2.h
> > @@ -30,6 +30,20 @@ struct StreamConfiguration;
> >   class CIO2Device
> >   {
> >   public:
> > +	/*
> > +	 * This many internal buffers for the CIO2 ensures that the pipeline
> > +	 * runs smoothly, without frame drops. This number considers:
> > +	 * - one buffer being DMA'ed to in CIO2
> > +	 * - one buffer programmed by the CIO2 as the next buffer
> > +	 * - one buffer under processing in ImgU
> > +	 * - one extra idle buffer queued to CIO2, to account for possible
> > +	 *   delays in requeuing the buffer from ImgU back to CIO2
> > +	 *
> > +	 * Transient situations can arise when one of the parts, CIO2 or ImgU,
> > +	 * finishes its processing first and experiences a lack of buffers, but
> > +	 * they will shortly after return to the state described above as the
> > +	 * other part catches up.
> > +	 */
> >   	static constexpr unsigned int kBufferCount = 4;
> >   	CIO2Device();
> > @@ -48,7 +62,7 @@ public:
> >   	V4L2SubdeviceFormat getSensorFormat(const std::vector<unsigned int> &mbusCodes,
> >   					    const Size &size) const;
> > -	int start();
> > +	int start(unsigned int bufferSlotCount);
> >   	int stop();
> >   	CameraSensor *sensor() { return sensor_.get(); }
> > diff --git a/src/libcamera/pipeline/ipu3/imgu.cpp b/src/libcamera/pipeline/ipu3/imgu.cpp
> > index 531879f1..fa920d87 100644
> > --- a/src/libcamera/pipeline/ipu3/imgu.cpp
> > +++ b/src/libcamera/pipeline/ipu3/imgu.cpp
> > @@ -576,22 +576,22 @@ int ImgUDevice::configureVideoDevice(V4L2VideoDevice *dev, unsigned int pad,
> >   /**
> >    * \brief Allocate buffers for all the ImgU video devices
> >    */
> > -int ImgUDevice::allocateBuffers(unsigned int bufferCount)
> > +int ImgUDevice::allocateBuffers(unsigned int bufferSlotCount)
> >   {
> >   	/* Share buffers between CIO2 output and ImgU input. */
> > -	int ret = input_->importBuffers(bufferCount);
> > +	int ret = input_->importBuffers(bufferSlotCount);
> >   	if (ret) {
> >   		LOG(IPU3, Error) << "Failed to import ImgU input buffers";
> >   		return ret;
> >   	}
> > -	ret = param_->allocateBuffers(bufferCount, &paramBuffers_);
> > +	ret = param_->allocateBuffers(kImgUInternalBufferCount, &paramBuffers_);
> >   	if (ret < 0) {
> >   		LOG(IPU3, Error) << "Failed to allocate ImgU param buffers";
> >   		goto error;
> >   	}
> > -	ret = stat_->allocateBuffers(bufferCount, &statBuffers_);
> > +	ret = stat_->allocateBuffers(kImgUInternalBufferCount, &statBuffers_);
> >   	if (ret < 0) {
> >   		LOG(IPU3, Error) << "Failed to allocate ImgU stat buffers";
> >   		goto error;
> > @@ -602,13 +602,13 @@ int ImgUDevice::allocateBuffers(unsigned int bufferCount)
> >   	 * corresponding stream is active or inactive, as the driver needs
> >   	 * buffers to be requested on the V4L2 devices in order to operate.
> >   	 */
> > -	ret = output_->importBuffers(bufferCount);
> > +	ret = output_->importBuffers(bufferSlotCount);
> >   	if (ret < 0) {
> >   		LOG(IPU3, Error) << "Failed to import ImgU output buffers";
> >   		goto error;
> >   	}
> > -	ret = viewfinder_->importBuffers(bufferCount);
> > +	ret = viewfinder_->importBuffers(bufferSlotCount);
> >   	if (ret < 0) {
> >   		LOG(IPU3, Error) << "Failed to import ImgU viewfinder buffers";
> >   		goto error;
> > diff --git a/src/libcamera/pipeline/ipu3/imgu.h b/src/libcamera/pipeline/ipu3/imgu.h
> > index 0af4dd8a..85873961 100644
> > --- a/src/libcamera/pipeline/ipu3/imgu.h
> > +++ b/src/libcamera/pipeline/ipu3/imgu.h
> > @@ -84,7 +84,7 @@ public:
> >   					    outputFormat);
> >   	}
> > -	int allocateBuffers(unsigned int bufferCount);
> > +	int allocateBuffers(unsigned int bufferSlotCount);
> >   	void freeBuffers();
> >   	int start();
> > @@ -119,6 +119,19 @@ private:
> >   	std::string name_;
> >   	MediaDevice *media_;
> > +
> > +	/*
> > +	 * This many internal buffers (or rather parameter and statistics buffer
> > +	 * pairs) for the ImgU ensures that the pipeline runs smoothly, without
> > +	 * frame drops. This number considers:
> > +	 * - three buffers queued to the CIO2 (Since these buffers are bound to
> > +	 *   CIO2 buffers before queuing to the CIO2)
> > +	 * - one buffer under processing in ImgU
> > +	 *
> > +	 * \todo Update this number when we make these buffers only get added to
> > +	 * the FrameInfo after the raw buffers are dequeued from CIO2.
> > +	 */
> > +	static constexpr unsigned int kImgUInternalBufferCount = 4;
> >   };
> >   } /* namespace libcamera */
> > diff --git a/src/libcamera/pipeline/ipu3/ipu3.cpp b/src/libcamera/pipeline/ipu3/ipu3.cpp
> > index bab2db65..4d8fcfeb 100644
> > --- a/src/libcamera/pipeline/ipu3/ipu3.cpp
> > +++ b/src/libcamera/pipeline/ipu3/ipu3.cpp
> > @@ -160,7 +160,7 @@ private:
> >   	int updateControls(IPU3CameraData *data);
> >   	int registerCameras();
> > -	int allocateBuffers(Camera *camera);
> > +	int allocateBuffers(Camera *camera, unsigned int bufferSlotCount);
> >   	int freeBuffers(Camera *camera);
> >   	ImgUDevice imgu0_;
> > @@ -169,6 +169,8 @@ private:
> >   	MediaDevice *imguMediaDev_;
> >   	std::vector<IPABuffer> ipaBuffers_;
> > +
> > +	static constexpr unsigned int kIPU3BufferSlotCount = 16;
> >   };
> >   IPU3CameraConfiguration::IPU3CameraConfiguration(IPU3CameraData *data)
> > @@ -710,20 +712,14 @@ int PipelineHandlerIPU3::exportFrameBuffers(Camera *camera, Stream *stream,
> >    * In order to be able to start the 'viewfinder' and 'stat' nodes, we need
> >    * memory to be reserved.
> >    */
> > -int PipelineHandlerIPU3::allocateBuffers(Camera *camera)
> > +int PipelineHandlerIPU3::allocateBuffers(Camera *camera,
> > +					 unsigned int bufferSlotCount)
> >   {
> >   	IPU3CameraData *data = cameraData(camera);
> >   	ImgUDevice *imgu = data->imgu_;
> > -	unsigned int bufferCount;
> >   	int ret;
> > -	bufferCount = std::max({
> > -		data->outStream_.configuration().bufferCount,
> > -		data->vfStream_.configuration().bufferCount,
> > -		data->rawStream_.configuration().bufferCount,
> > -	});
> > -
> > -	ret = imgu->allocateBuffers(bufferCount);
> > +	ret = imgu->allocateBuffers(bufferSlotCount);
> >   	if (ret < 0)
> >   		return ret;
> > @@ -781,7 +777,7 @@ int PipelineHandlerIPU3::start(Camera *camera, [[maybe_unused]] const ControlLis
> >   		return ret;
> >   	/* Allocate buffers for internal pipeline usage. */
> > -	ret = allocateBuffers(camera);
> > +	ret = allocateBuffers(camera, kIPU3BufferSlotCount);
> >   	if (ret)
> >   		return ret;
> > @@ -795,7 +791,7 @@ int PipelineHandlerIPU3::start(Camera *camera, [[maybe_unused]] const ControlLis
> >   	 * Start the ImgU video devices, buffers will be queued to the
> >   	 * ImgU output and viewfinder when requests will be queued.
> >   	 */
> > -	ret = cio2->start();
> > +	ret = cio2->start(kIPU3BufferSlotCount);
> >   	if (ret)
> >   		goto error;
>