From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Lists linaro-kernel <linaro-kernel@lists.linaro.org>,
Linux PM <linux-pm@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Steve Muckle <smuckle.linux@gmail.com>,
Juri Lelli <juri.lelli@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
eas-dev@lists.linaro.org
Subject: Re: [RFC 5/9] sched: cpufreq: remove smp_processor_id() in remote paths
Date: Tue, 11 Apr 2017 16:00:28 +0200 [thread overview]
Message-ID: <CAJZ5v0iQ4X=Vt54EvJce9R9rPhtVqvznte8=HoQ_UOAZ1fQj2g@mail.gmail.com> (raw)
In-Reply-To: <20170411103556.GC13627@vireshk-i7>
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. :-)
>> > 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.
Thanks,
Rafael
next prev parent reply other threads:[~2017-04-11 14:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-09 11:45 [RFC 0/9] cpufreq: schedutil: Allow remote wakeups Viresh Kumar
2017-03-09 11:45 ` [RFC 1/9] sched: cpufreq: add cpu to update_util_data Viresh Kumar
2017-03-29 21:18 ` Rafael J. Wysocki
2017-03-09 11:45 ` [RFC 2/9] irq_work: add irq_work_queue_on for !CONFIG_SMP Viresh Kumar
2017-03-29 21:20 ` Rafael J. Wysocki
2017-03-09 11:45 ` [RFC 3/9] cpufreq: Add dvfs_possible_from_any_cpu policy flag Viresh Kumar
2017-03-29 21:22 ` Rafael J. Wysocki
2017-03-09 11:45 ` [RFC 4/9] sched: cpufreq: extend irq work to support fast switches Viresh Kumar
2017-03-29 21:25 ` Rafael J. Wysocki
2017-03-09 11:45 ` [RFC 5/9] sched: cpufreq: remove smp_processor_id() in remote paths Viresh Kumar
2017-03-29 21:28 ` Rafael J. Wysocki
2017-04-11 10:35 ` Viresh Kumar
2017-04-11 14:00 ` Rafael J. Wysocki [this message]
2017-04-12 14:26 ` Viresh Kumar
2017-04-12 22:53 ` Rafael J. Wysocki
2017-03-09 11:45 ` [RFC 6/9] sched: cpufreq: detect, process remote callbacks Viresh Kumar
2017-03-29 21:58 ` Rafael J. Wysocki
2017-03-09 11:45 ` [RFC 7/9] cpufreq: governor: support scheduler cpufreq callbacks on remote CPUs Viresh Kumar
2017-03-29 22:14 ` Rafael J. Wysocki
2017-04-11 11:06 ` Viresh Kumar
2017-03-09 11:45 ` [RFC 8/9] intel_pstate: ignore " Viresh Kumar
2017-03-29 22:15 ` Rafael J. Wysocki
2017-03-09 11:45 ` [RFC 9/9] sched: cpufreq: enable remote sched cpufreq callbacks Viresh Kumar
2017-03-15 11:45 ` [RFC 0/9] cpufreq: schedutil: Allow remote wakeups Rafael J. Wysocki
2017-03-16 3:09 ` Viresh Kumar
2017-03-16 10:04 ` Rafael J. Wysocki
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