From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steve Muckle <steve.muckle@linaro.org>,
Ingo Molnar <mingo@redhat.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Juri Lelli <Juri.Lelli@arm.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Michael Turquette <mturquette@baylibre.com>,
Ricky Liang <jcliang@chromium.org>
Subject: Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection
Date: Thu, 25 Feb 2016 22:08:48 +0100 [thread overview]
Message-ID: <1792311.cuUNhUde5n@vostro.rjw.lan> (raw)
In-Reply-To: <20160225092837.GD6357@twins.programming.kicks-ass.net>
On Thursday, February 25, 2016 10:28:37 AM Peter Zijlstra wrote:
> On Thu, Feb 25, 2016 at 04:55:57AM +0100, Rafael J. Wysocki wrote:
> > > +static void dummy(void *info) {}
> > > +
> > > +static int cpufreq_sched_stop(struct cpufreq_policy *policy)
> > > +{
> > > + struct gov_data *gd = policy->governor_data;
> > > + int cpu;
> > > +
> > > + /*
> > > + * The schedfreq static key is managed here so the global schedfreq
> > > + * lock must be taken - a per-policy lock such as policy->rwsem is
> > > + * not sufficient.
> > > + */
> > > + mutex_lock(&gov_enable_lock);
> > > +
> > > + /*
> > > + * The governor stop path may or may not hold policy->rwsem. There
> > > + * must be synchronization with the slow path however.
> > > + */
> > > + mutex_lock(&gd->slowpath_lock);
> > > +
> > > + /*
> > > + * Stop new entries into the hot path for all CPUs. This will
> > > + * potentially affect other policies which are still running but
> > > + * this is an infrequent operation.
> > > + */
> > > + static_key_slow_dec(&__sched_freq);
> > > + enabled_policies--;
> > > +
> > > + /*
> > > + * Ensure that all CPUs currently part of this policy are out
> > > + * of the hot path so that if this policy exits we can free gd.
> > > + */
> > > + preempt_disable();
> > > + smp_call_function_many(policy->cpus, dummy, NULL, true);
> > > + preempt_enable();
> >
> > I'm not sure how this works, can you please tell me?
>
> I think it relies on the fact that rq->lock disables IRQs, so if we've
> managed to IPI all relevant CPUs, it means they cannot be inside a
> rq->lock section.
>
> Its vile though; one should not spray IPIs if one can avoid it. Such
> things are much better done with RCU. Sure sync_sched() takes a little
> longer, but this isn't a fast path by any measure.
I see, thanks!
BTW, when cpufreq_update_util() callbacks are removed, I use synchronize_rcu()
to wait for the running ones, but would it be better to use synchronize_sched()
in there instead?
Thanks,
Rafael
next prev parent reply other threads:[~2016-02-25 21:07 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 1:22 [RFCv7 PATCH 00/10] sched: scheduler-driven CPU frequency selection Steve Muckle
2016-02-23 1:22 ` [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at current frequency Steve Muckle
2016-02-23 1:41 ` Rafael J. Wysocki
2016-02-23 9:19 ` Peter Zijlstra
2016-02-26 1:37 ` Rafael J. Wysocki
2016-02-26 9:14 ` Peter Zijlstra
2016-02-23 1:22 ` [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow Steve Muckle
2016-02-23 1:31 ` Rafael J. Wysocki
2016-02-26 0:50 ` Michael Turquette
2016-02-26 1:07 ` Steve Muckle
2016-02-26 1:16 ` Rafael J. Wysocki
[not found] ` <20160226185503.2278.20479@quark.deferred.io>
2016-02-26 21:00 ` Rafael J. Wysocki
2016-02-23 1:22 ` [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection Steve Muckle
2016-02-25 3:55 ` Rafael J. Wysocki
2016-02-25 9:21 ` Peter Zijlstra
2016-02-25 21:04 ` Rafael J. Wysocki
2016-02-25 9:28 ` Peter Zijlstra
2016-02-25 21:08 ` Rafael J. Wysocki [this message]
2016-02-26 9:18 ` Peter Zijlstra
2016-02-27 0:08 ` Rafael J. Wysocki
2016-03-01 12:57 ` Peter Zijlstra
2016-03-01 19:44 ` Rafael J. Wysocki
2016-02-25 11:04 ` Rafael J. Wysocki
2016-02-26 0:34 ` Steve Muckle
2016-02-27 2:39 ` Rafael J. Wysocki
2016-02-27 4:17 ` Steve Muckle
2016-02-28 2:26 ` Rafael J. Wysocki
2016-03-01 14:31 ` Peter Zijlstra
2016-03-01 20:32 ` Rafael J. Wysocki
2016-03-01 13:26 ` Peter Zijlstra
2016-03-01 13:17 ` Peter Zijlstra
2016-03-02 7:49 ` Michael Turquette
2016-03-03 2:49 ` Rafael J. Wysocki
2016-03-03 3:50 ` Steve Muckle
2016-03-03 9:34 ` Juri Lelli
2016-03-03 13:03 ` Peter Zijlstra
2016-03-03 14:21 ` Ingo Molnar
2016-02-23 1:22 ` [RFCv7 PATCH 04/10] sched/fair: add triggers for OPP change requests Steve Muckle
2016-03-01 6:51 ` Ricky Liang
2016-03-03 3:55 ` Steve Muckle
2016-02-23 1:22 ` [RFCv7 PATCH 05/10] sched/{core,fair}: trigger OPP change request on fork() Steve Muckle
2016-02-23 1:22 ` [RFCv7 PATCH 06/10] sched/fair: cpufreq_sched triggers for load balancing Steve Muckle
2016-02-23 1:22 ` [RFCv7 PATCH 07/10] sched/fair: jump to max OPP when crossing UP threshold Steve Muckle
2016-02-23 1:22 ` [RFCv7 PATCH 08/10] sched: remove call of sched_avg_update from sched_rt_avg_update Steve Muckle
2016-02-23 1:22 ` [RFCv7 PATCH 09/10] sched/deadline: split rt_avg in 2 distincts metrics Steve Muckle
2016-02-23 1:22 ` [RFCv7 PATCH 10/10] sched: rt scheduler sets capacity requirement Steve Muckle
2016-02-23 1:33 ` [RFCv7 PATCH 00/10] sched: scheduler-driven CPU frequency selection Steve Muckle
2016-03-30 0:45 ` Yuyang Du
2016-03-31 1:35 ` Steve Muckle
2016-03-30 20:22 ` Yuyang Du
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