From: Michael Turquette <mturquette@baylibre.com>
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 Mailing List <linux-kernel@vger.kernel.org>,
"linux-pm@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>,
Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow
Date: Thu, 25 Feb 2016 16:50:29 -0800 [thread overview]
Message-ID: <20160226005029.2278.38972@quark.deferred.io> (raw)
In-Reply-To: <CAJZ5v0gM56y0+_SCV5RDQzWWJxS_aNWWpi8ZrcGtjZo+fH2uUA@mail.gmail.com>
Quoting Rafael J. Wysocki (2016-02-22 17:31:09)
> On Tue, Feb 23, 2016 at 2:22 AM, Steve Muckle <steve.muckle@linaro.org> wrote:
> > From: Michael Turquette <mturquette@baylibre.com>
> >
> > Some architectures and platforms perform CPU frequency transitions
> > through a non-blocking method, while some might block or sleep. Even
> > when frequency transitions do not block or sleep they may be very slow.
> > This distinction is important when trying to change frequency from
> > a non-interruptible context in a scheduler hot path.
> >
> > Describe this distinction with a cpufreq driver flag,
> > CPUFREQ_DRIVER_FAST. The default is to not have this flag set,
> > thus erring on the side of caution.
> >
> > cpufreq_driver_is_slow() is also introduced in this patch. Setting
> > the above flag will allow this function to return false.
> >
> > [smuckle@linaro.org: change flag/API to include drivers that are too
> > slow for scheduler hot paths, in addition to those that block/sleep]
> >
> > Cc: Rafael J. Wysocki <rafael@kernel.org>
> > Cc: Viresh Kumar <viresh.kumar@linaro.org>
> > Signed-off-by: Michael Turquette <mturquette@baylibre.com>
> > Signed-off-by: Steve Muckle <smuckle@linaro.org>
>
> Something more sophisticated than this is needed, because one driver
> may actually be able to do "fast" switching in some cases and may not
> be able to do that in other cases.
Those drivers can set the flag dynamically when they probe based on
their ACPI tables.
>
> For example, in the acpi-cpufreq case all depends on what's there in
> the ACPI tables.
It's all a moot point until the locking in cpufreq is changed. Until
those changes are made it is a bad idea to call cpufreq_driver_target()
from schedule() context, regardless of the underlying hardware, and all
platforms should kick that work out to the kthread.
Regards,
Mike
>
> Thanks,
> Rafael
next prev parent reply other threads:[~2016-02-26 1:00 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 [this message]
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
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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