Messages in this thread | | | Date | Thu, 30 Nov 2017 17:45:01 +0100 | From | Juri Lelli <> | Subject | Re: [PATCH v3 1/6] cpufreq: schedutil: reset sg_cpus's flags at IDLE enter |
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On 30/11/17 16:19, Patrick Bellasi wrote: > On 30-Nov 17:02, Juri Lelli wrote: > > On 30/11/17 15:41, Patrick Bellasi wrote: > > > On 30-Nov 14:12, Juri Lelli wrote: > > > > Hi, > > > > > > > > On 30/11/17 11:47, Patrick Bellasi wrote: > > > > > > > > [...] > > > > > > > > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > > > > > index 2f52ec0f1539..67339ccb5595 100644 > > > > > --- a/kernel/sched/cpufreq_schedutil.c > > > > > +++ b/kernel/sched/cpufreq_schedutil.c > > > > > @@ -347,6 +347,12 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time, > > > > > > > > > > sg_cpu->util = util; > > > > > sg_cpu->max = max; > > > > > + > > > > > + /* CPU is entering IDLE, reset flags without triggering an update */ > > > > > + if (unlikely(flags & SCHED_CPUFREQ_IDLE)) { > > > > > + sg_cpu->flags = 0; > > > > > + goto done; > > > > > + } > > > > > > > > Looks good for now. I'm just thinking that we will happen for DL, as a > > > > CPU that still "has" a sleeping task is not going to be really idle > > > > until the 0-lag time. > > > > > > AFAIU, for the time being, DL already cannot really rely on this flag > > > for its behaviors to be correct. Indeed, flags are reset as soon as > > > a FAIR task wakes up and it's enqueued. > > > > Right, and your flags ORing patch should help with this. > > > > > > > > Only once your DL integration patches are in, we do not depends on > > > flags anymore since DL will report a ceratain utilization up to the > > > 0-lag time, isn't it? > > > > Utilization won't decrease until 0-lag time, correct. > > Then IMO with your DL patches the DL class don't need the flags > anymore since schedutil will know (and account) for the > utlization required by the DL tasks. Isn't it? > > > I was just wondering if resetting flags before that time (when a CPU > > enters idle) might be an issue. > > If the above is correct, then flags will be used only for the RT class (and > IO boosting)... and thus this patch will still be useful as it is now: > meaning that once the idle task is selected we do not care anymore > about RT and IOBoosting (only). > > > > If that's the case, I would say that the flags will be used only to > > > jump to the max OPP for RT tasks. Thus, this patch should still be valid. > > > > > > > I guess we could move this at that point in time? > > > > > > Not sure what you mean here. Right now the new SCHED_CPUFREQ_IDLE flag > > > is notified only by idle tasks. That's the only code path where we are > > > sure the CPU is entering IDLE. > > > > > > > W.r.t. the possible issue above, I was thinking that we might want to > > reset flags at 0-lag time for DL (if CPU is still idle). Anyway, two > > distinct set of patches. Who gets in last will have to ponder the thing > > a little bit more. :) > > Perhaps I'm still a bit confused but, to me, it seems that with your > patches we completely fix DL but we still can use this exact same > patch just for RT tasks.
We don't use the flags for bailing out during aggregation, so it should be ok for DL yes.
Thanks,
Juri
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