From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Steve Muckle <steve.muckle@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.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>,
Juri Lelli <juri.lelli@arm.com>
Subject: Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection
Date: Thu, 25 Feb 2016 12:04 +0100 [thread overview]
Message-ID: <6080807.PFHSVxFDKN@vostro.rjw.lan> (raw)
In-Reply-To: <8427745.Y8N2bqC3SO@vostro.rjw.lan>
On Thursday, February 25, 2016 04:55:57 AM Rafael J. Wysocki wrote:
> Hi,
>
[cut]
> > + while (true) {
> > + set_current_state(TASK_INTERRUPTIBLE);
> > + if (kthread_should_stop()) {
> > + set_current_state(TASK_RUNNING);
> > + break;
> > + }
> > + new_request = gd->requested_freq;
> > + if (!gd->enabled || new_request == last_request) {
>
> This generally is a mistake.
>
> You can't assume that if you had requested a CPU to enter a specific P-state,
> that state was actually entered. In the platform-coordinated case the hardware
> (or firmware) may choose to ignore your request and you won't be told about
> that.
>
> For this reason, you generally need to make the request every time even if it
> is identical to the previous one. Even in the one-CPU-per-policy case there
> may be HW coordination you don't know about.
Please scratch this bit, actually (and analogous comments below).
It is reasonable to expect that the platform will remember your last request,
so you don't have to repeat it.
Which means that I can optimize the schedutil thing somewhat. :-)
Thanks,
Rafael
next prev parent reply other threads:[~2016-02-25 11:02 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
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 [this message]
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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