Messages in this thread | | | Date | Wed, 12 Apr 2017 19:56:28 +0530 | From | Viresh Kumar <> | Subject | Re: [RFC 5/9] sched: cpufreq: remove smp_processor_id() in remote paths |
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On 11-04-17, 16:00, Rafael J. Wysocki wrote: > On Tue, Apr 11, 2017 at 12:35 PM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > > On 29-03-17, 23:28, Rafael J. Wysocki wrote: > >> On Thursday, March 09, 2017 05:15:15 PM Viresh Kumar wrote: > >> > @@ -216,7 +216,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, > >> > if (flags & SCHED_CPUFREQ_RT_DL) { > >> > next_f = policy->cpuinfo.max_freq; > >> > } else { > >> > - sugov_get_util(&util, &max); > >> > + sugov_get_util(&util, &max, hook->cpu); > >> > >> Why is this not racy? > > > > Why would reading the utilization values be racy? The only dynamic value here is > > "util_avg" and I am not sure if reading it is racy. > > > > But, this whole routine has races which I ignored as we may end up updating > > frequency simultaneously from two threads. > > Those races aren't there if we don't update cross-CPU, which is my point. :-)
Of course. There are no races without this series.
> >> > sugov_iowait_boost(sg_cpu, &util, &max); > >> > next_f = get_next_freq(sg_policy, util, max); > >> > } > >> > @@ -272,7 +272,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time, > >> > unsigned long util, max; > >> > unsigned int next_f; > >> > > >> > - sugov_get_util(&util, &max); > >> > + sugov_get_util(&util, &max, hook->cpu); > >> > > >> > >> And here? > >> > >> > raw_spin_lock(&sg_policy->update_lock); > > > > The lock prevents the same here though. > > > > So, if we are going to use this series, then we can use the same update-lock in > > case of single cpu per policies as well. > > No, we can't. > > The lock is unavoidable in the mulit-CPU policies case, but there's no > way I will agree on using a lock in the single-CPU case.
How do you suggest to avoid the locking here then ? Some atomic variable read/write as done in cpufreq_governor.c ?
-- viresh
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