Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 27 Jun 2017 18:08:43 +0200 | Subject | Re: [PATCH] cpufreq: dt: Set default policy->transition_delay_ns |
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Hi,
On Tue, Jun 27, 2017 at 6:20 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > On 27-06-17, 02:15, Rafael J. Wysocki wrote: >> On Monday, May 22, 2017 04:57:27 PM Viresh Kumar wrote: >> > On 22-05-17, 19:17, Leo Yan wrote: >> > > This afternoon Amit pointed me for this patch, should fix as below? >> > > Otherwise it seems directly assign the same value from unit 'ns' to >> > > 'us' but without any value conversion. >> > > >> > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c >> > > index 76877a6..dcc90fc 100644 >> > > --- a/kernel/sched/cpufreq_schedutil.c >> > > +++ b/kernel/sched/cpufreq_schedutil.c >> > > @@ -538,7 +538,7 @@ static int sugov_init(struct cpufreq_policy *policy) >> > > unsigned int lat; >> > > >> > > tunables->rate_limit_us = LATENCY_MULTIPLIER; >> > > - lat = policy->cpuinfo.transition_latency / NSEC_PER_USEC; > > I think the above line is just fine and the below one is incorrect, as > we wanted to convert transition latency to usec here (i.e. in the > units of rate_limit_us). > >> > > + lat = policy->cpuinfo.transition_latency / NSEC_PER_MSEC; >> > > if (lat) >> > > tunables->rate_limit_us *= lat; >> > > } >> > >> > I will let Rafael comment in as well. NSEC_PER_USEC is used in the >> > earlier governors as well (ondemand/conservative) in exactly the same >> > way as schedutil is using. >> >> The reason why it is used by schedutil is because the other governors used it >> that way. IOW, doesn't matter. :-) > > But I feel the value of LATENCY_MULTIPLIER (1000) is way too high. It currently > says that if freq-switching takes time X, then we should wait for 999X time > before we change the freq again. > > Perhaps LATENCY_MULTIPLIER should be just 10 or 20 here. For a platform with > transition_latency 500 us, rate_limit_us comes to 500 ms. Which is absurd. We > ideally want it to be around 10-20 ms here. And compared to other ARM platforms, > 500 us transition_latency is very low. It normally is around 1-3 ms for ARM32 > platforms. > > @Rafael: Will it be fine to lower down the value of LATENCY_MULTIPLIER?
We can do that, but then I think we need to compensate for the change in the old governors code or there may be surprises.
Thanks, Rafael
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