On 5/27/20 2:48 PM, Benjamin GAIGNARD wrote: > > > On 5/27/20 2:22 PM, Vincent Guittot wrote: >> On Wed, 27 May 2020 at 13:17, Benjamin GAIGNARD >> <benjamin.gaignard@xxxxxx> wrote: >>> >>> >>> On 5/27/20 12:09 PM, Valentin Schneider wrote: >>>> Hi Benjamin, >>>> >>>> On 26/05/20 16:16, Benjamin Gaignard wrote: >>>>> 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 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. >> IMHO, the only way to ensure a min frequency for anything else than a >> thread is to use freq_qos_add_request() just like cpufreq cooling >> device but for the opposite QoS. This can be applied only on the >> frequency domain of the CPU which handles the interrupt. > I will give a try with this idea. > Thanks. Adding freq_qos_add_request(FREQ_QOS_MIN) when starting streaming frames solve my problem. I remove the request at the end of the streaming to restore the default value. Benjamin >> Have you also checked the wakeup latency of your idle state ? > It just could go in WFI so latency should be minimal. >> >>> >>>>> 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(+) >
