On Monday, May 14, 2018 5:45:23 PM CEST Yu Chen wrote: > On Sun, May 13, 2018 at 11:30:52AM +0200, Rafael J. Wysocki wrote: > > On Saturday, May 5, 2018 1:53:22 PM CEST Chen Yu wrote: > > > According to current implementation of acpi_pad driver, > > > it does not make sense to spawn any power saving threads > > > on the cpus which are already idle - it might bring > > > unnecessary overhead on these idle cpus and causes power > > > waste. So verify the condition that if the number of 'busy' > > > cpus exceeds the amount of the 'forced idle' cpus is met. > > > This is applicable due to round-robin attribute of the > > > power saving threads, otherwise ignore the setting/ACPI > > > notification. > > > > OK, but CPUs are busy, because they are running tasks. If acpi_pad > > kthreads run on them, the tasks they are running will migrate to the > > currently idle CPUs (unless they have specific CPU affinity) and the > > throttling will not really be effective. > > > OK, I think this makes sense, I missed the load balance scenario. > > I would think that acpi_pad should ensure that the requested number of > > CPUs will not run anything other than throttling kthreads. Isn't that > > the case? > > > Do you mean, we should check if the number of 'idle'(rather than the 'busy' one > in this patch) cpus is larger than the requested one? Then I think we should also > add a patch to use the play_idle() as power_clamp to treat the throttling kthreads > as idle threads thus to stop system tick. Such as the patch Jacob proposed: I wonder if that can be switched over to the new idle injection framework added recently? Thanks, Rafael
