On 6 June 2018 at 11:59, Vincent Guittot <vincent.guit...@linaro.org> wrote: > On 6 June 2018 at 11:44, Quentin Perret <quentin.per...@arm.com> wrote: >> On Tuesday 05 Jun 2018 at 16:18:09 (+0200), Peter Zijlstra wrote:
[snip] >>> >>> > As you mentioned, scale_rt_capacity give the remaining capacity for >>> > cfs and it will behave like cfs util_avg now that it uses PELT. So as >>> > long as cfs util_avg < scale_rt_capacity(we probably need a margin) >>> > we keep using dl bandwidth + cfs util_avg + rt util_avg for selecting >>> > OPP because we have remaining spare capacity but if cfs util_avg == >>> > scale_rt_capacity, we make sure to use max OPP. >>> >>> Good point, when cfs-util < cfs-cap then there is idle time and the util >>> number is 'right', when cfs-util == cfs-cap we're overcommitted and >>> should go max. >>> >>> Since the util and cap values are aligned that should track nicely. I have re run my tests and and the results seem to be ok so far. I'm going to clean up a bit the code used for the test and sent a new version of the proposal >> >> So Vincent proposed to have a margin between cfs util and cfs cap to be >> sure there is a little bit of idle time. This is _exactly_ what the >> overutilized flag in EAS does. That would actually make a lot of sense >> to use that flag in schedutil. The idea is basically to say, if there >> isn't enough idle time on all CPUs, the util signal are kinda wrong, so >> let's not make any decisions (task placement or OPP selection) based on >> that. If overutilized, go to max freq. Does that make sense ? > > Yes it's similar to the overutilized except that > - this is done per cpu and whereas overutilization is for the whole system > - the test is done at every freq update and not only during some cfs > event and it uses the last up to date value and not a periodically > updated snapshot of the value > - this is done also without EAS > > Then for the margin, it has to be discussed if it is really needed or not > >> >> Thanks, >> Quentin
