[libcamera-devel] [PATCH v6 6/6] ipa: raspberrypi: Rate-limit the controller algorithms

[David Plowman]

Hi Naush

Thanks for this patch. For reasons unknown, gmail seems to have tacked
it on as a reply to the cover note...

On Mon, 10 May 2021 at 10:59, Naushir Patuck <naush at raspberrypi.com> wrote:
>
> The controller algorithms currently run on every frame provided to the
> IPA by the pipeline handler. This may be undesirable for very fast fps
> operating modes where it could significantly increase the computation
> cycles (per unit time) without providing any significant changes to the
> IQ parameters. The added latencies could also cause dropped frames.
>
> Pass the FrameBuffer timestamp to the IPA through the controls. This
> timestamp will be used to rate-limit the controller algorithms to run
> with a minimum inter-frame time given by a compile time constant,
> currently set to 16.66ms. On startup, we don't rate-limit the algorithms
> until after the number of frames required for convergence.
>
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> ---
>  src/ipa/raspberrypi/raspberrypi.cpp           | 42 +++++++++++++++++--
>  .../pipeline/raspberrypi/raspberrypi.cpp      |  5 +++
>  2 files changed, 43 insertions(+), 4 deletions(-)
>
> diff --git a/src/ipa/raspberrypi/raspberrypi.cpp b/src/ipa/raspberrypi/raspberrypi.cpp
> index 07409621a03a..52d91db282ea 100644
> --- a/src/ipa/raspberrypi/raspberrypi.cpp
> +++ b/src/ipa/raspberrypi/raspberrypi.cpp
> @@ -61,6 +61,14 @@ constexpr unsigned int DefaultExposureTime = 20000;
>  constexpr double defaultMinFrameDuration = 1e6 / 30.0;
>  constexpr double defaultMaxFrameDuration = 1e6 / 0.01;
>
> +/*
> + * Determine the minimum allowable inter-frame duration (in us) to run the
> + * controller algorithms. If the pipeline handler provider frames at a rate
> + * higher than this, we rate-limit the controller Prepare() and Process() calls
> + * to lower than or equal to this rate.
> + */
> +constexpr double controllerMinFrameDuration = 1e6 / 60.0;
> +
>  LOG_DEFINE_CATEGORY(IPARPI)
>
>  class IPARPi : public ipa::RPi::IPARPiInterface
> @@ -68,7 +76,7 @@ class IPARPi : public ipa::RPi::IPARPiInterface
>  public:
>         IPARPi()
>                 : controller_(), frameCount_(0), checkCount_(0), mistrustCount_(0),
> -                 lsTable_(nullptr), firstStart_(true)
> +                 lastRunTimestamp_(0), lsTable_(nullptr), firstStart_(true)
>         {
>         }
>
> @@ -146,6 +154,12 @@ private:
>         /* Number of frames that need to be dropped on startup. */
>         unsigned int dropFrameCount_;
>
> +       /* Frame timestamp for the last run of the controller. */
> +       uint64_t lastRunTimestamp_;
> +
> +       /* Do we run a Controller::process() for this frame? */
> +       bool processPending_;
> +
>         /* LS table allocation passed in from the pipeline handler. */
>         FileDescriptor lsTableHandle_;
>         void *lsTable_;
> @@ -262,6 +276,7 @@ void IPARPi::start(const ControlList &controls, ipa::RPi::StartConfig *startConf
>         startConfig->dropFrameCount = dropFrameCount_;
>
>         firstStart_ = false;
> +       lastRunTimestamp_ = 0;
>  }
>
>  void IPARPi::setMode(const CameraSensorInfo &sensorInfo)
> @@ -406,7 +421,7 @@ void IPARPi::signalStatReady(uint32_t bufferId)
>  {
>         if (++checkCount_ != frameCount_) /* assert here? */
>                 LOG(IPARPI, Error) << "WARNING: Prepare/Process mismatch!!!";
> -       if (frameCount_ > mistrustCount_)
> +       if (processPending_ && frameCount_ > mistrustCount_)

I guess the only thing that caused my brain to pause for a moment was
the need to convince myself that processPending_ can't be
uninitialised. But prepareISP always sets it and must run before this,
so we're all good...

>                 processStats(bufferId);
>
>         reportMetadata();
> @@ -894,10 +909,11 @@ void IPARPi::returnEmbeddedBuffer(unsigned int bufferId)
>
>  void IPARPi::prepareISP(const ipa::RPi::ISPConfig &data)
>  {
> +       int64_t frameTimestamp = data.controls.get(controls::SensorTimestamp);

Just wondering if there's any possibility that the first time stamp
could be zero, thereby matching the initial value of lastRunTimestamp.
The result would be that we start running the control algos a frame or
so late. If we're happy that this doesn't happen, then I'm OK with it
too.

> +       RPiController::Metadata lastMetadata;
>         Span<uint8_t> embeddedBuffer;
>
> -       rpiMetadata_.Clear();
> -
> +       lastMetadata = std::move(rpiMetadata_);
>         fillDeviceStatus(data.controls);
>
>         if (data.embeddedBufferPresent) {
> @@ -920,6 +936,24 @@ void IPARPi::prepareISP(const ipa::RPi::ISPConfig &data)
>         if (data.embeddedBufferPresent)
>                 returnEmbeddedBuffer(data.embeddedBufferId);
>
> +       /* Allow a 10% margin on the comparison below. */
> +       constexpr double eps = controllerMinFrameDuration * 1e3 * 0.1;
> +       if (lastRunTimestamp_ && frameCount_ > dropFrameCount_ &&
> +           frameTimestamp - lastRunTimestamp_ + eps < controllerMinFrameDuration * 1e3) {

Might this be easier to read if we defined all these things in
nanoseconds right from the start? But I really can't get too worked up
over it!

Reviewed-by: David Plowman <david.plowman at raspberrypi.com>

Best regards
David

> +               /*
> +                * Ensure we merge the previous frame's metadata with the current
> +                * frame. This will not overwrite exposure/gain values for the
> +                * current frame, or any other bits of metadata that were added
> +                * in helper_->Prepare().
> +                */
> +               rpiMetadata_.Merge(lastMetadata);
> +               processPending_ = false;
> +               return;
> +       }
> +
> +       lastRunTimestamp_ = frameTimestamp;
> +       processPending_ = true;
> +
>         ControlList ctrls(ispCtrls_);
>
>         controller_.Prepare(&rpiMetadata_);
> diff --git a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> index b22564938cdc..d26ae2a9772a 100644
> --- a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> +++ b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> @@ -1426,6 +1426,11 @@ void RPiCameraData::unicamBufferDequeue(FrameBuffer *buffer)
>                  * DelayedControl and queue them along with the frame buffer.
>                  */
>                 ControlList ctrl = delayedCtrls_->get(buffer->metadata().sequence);
> +               /*
> +                * Add the frame timestamp to the ControlList for the IPA to use
> +                * as it does not receive the FrameBuffer object.
> +                */
> +               ctrl.set(controls::SensorTimestamp, buffer->metadata().timestamp);
>                 bayerQueue_.push({ buffer, std::move(ctrl) });
>         } else {
>                 embeddedQueue_.push(buffer);
> --
> 2.25.1
>
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