On 4/29/20 6:12 PM, Valentin Schneider wrote: > On 29/04/2020 16:57, Benjamin GAIGNARD wrote: >> >> On 4/29/20 5:50 PM, Rafael J. Wysocki wrote: >>> On Friday, April 24, 2020 1:40:55 PM CEST Benjamin Gaignard wrote: >>>> 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. >>> This seems to be addressing a use case that can be addressed with the help of >>> utilization clamps with less power overhead. >> Do mean clamping the policy frequencies ? I may have miss the API to do >> that... > IIUC Rafael is referring to uclamp, i.e. scheduler utilization clamping, see: > > https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#cpu > > The above describes the cgroup interface, note that you can also set clamps > per task (via sched_setattr()). > > One thing that comes to mind however is that schedutil only "sees" the clamps > of runnable tasks, and from reading your changelog you may not have moments > without any (i.e. gears are grinding in HW). You'd have to try boosting > (setting a high uclamp.min) whatever tasks you have on the software side and > see how it all behaves. Relying on userland side means that various applications need to be aware of this specific hardware case and fix it. I was hoping to find a solution in side the kernel to not impact the software side. > >>> Thanks! >>> >>> >>>
