On 27/05/20 14:11, Benjamin GAIGNARD wrote:

On 5/27/20 2:14 PM, Valentin Schneider wrote:

quoted

On 27/05/20 12:17, Benjamin GAIGNARD wrote:

quoted

On 5/27/20 12:09 PM, Valentin Schneider wrote:

quoted

Hi Benjamin,

On 26/05/20 16:16, Benjamin Gaignard wrote:

quoted

A first round [1] of discussions and suggestions have already be done on
this series but without found a solution to the problem. I resend it to
progress on this topic.

Apologies for sleeping on that previous thread.

So what had been suggested over there was to use uclamp to boost the
frequency of the handling thread; however if you use threaded IRQs you
get RT threads, which already get the max frequency by default (at least
with schedutil).

Does that not work for you, and if so, why?

That doesn't work because almost everything is done by the hardware blocks
without charge the CPU so the thread isn't running.

I'm not sure I follow; the frequency of the CPU doesn't matter while
your hardware blocks are spinning, right? AIUI what matters is running
your interrupt handler / action at max freq, which you get if you use
threaded IRQs and schedutil.

Yes but not limited to schedutil.
Given the latency needed to change of frequencies I think it could
already too late
to change the CPU frequency when handling the threaded interrupt.

Right, on my Juno the transition latency (i.e. worse case) is about
1.2ms; I can see that eating into your time budget, depending on the
framerate you're going for.

Vincent's got a point, if you can limit that max-freq-hold to a single
frequency domain, that would probably be a tad better.

Thanks for persisting through my questioning :-)

quoted

I think it would help if you could clarify which tasks / parts of your
pipeline you need running at high frequencies. The point is that setting
a QoS request affects all tasks, whereas we could be smarter and only
boost the required tasks.

What make us drop frames is that the threaded IRQ is scheduled too late.
The not thread part of the interrupt handler where we clear the
interrupt flags
is going fine but the thread part not.

quoted

quoted

I have done the
tests with schedutil
and ondemand scheduler (which is the one I'm targeting). I have no
issues when using
performance scheduler because it always keep the highest frequencies.

quoted

quoted

When start streaming from the sensor the CPU load could remain very low
because almost all the capture pipeline is done in hardware (i.e. without
using the CPU) and let believe to cpufreq governor that it could use lower
frequencies. If the governor decides to use a too low frequency that
becomes a problem when we need to acknowledge the interrupt during the
blanking time.
The delay to ack the interrupt and perform all the other actions before
the next frame is very short and doesn't allow to the cpufreq governor to
provide the required burst of power. That led to drop the half of the frames.

To avoid this problem, DCMI driver informs the cpufreq governors by adding
a cpufreq minimum load QoS resquest.

Benjamin

[1] https://lkml.org/lkml/2020/4/24/360

Benjamin Gaignard (3):
    PM: QoS: Introduce cpufreq minimum load QoS
    cpufreq: governor: Use minimum load QoS
    media: stm32-dcmi: Inform cpufreq governors about cpu load needs

   drivers/cpufreq/cpufreq_governor.c        |   5 +
   drivers/media/platform/stm32/stm32-dcmi.c |   8 ++
   include/linux/pm_qos.h                    |  12 ++
   kernel/power/qos.c                        | 213 ++++++++++++++++++++++++++++++
   4 files changed, 238 insertions(+)

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