From: Peter Zijlstra <peterz@infradead.org>
To: Steve Muckle <steve.muckle@linaro.org>
Cc: 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>,
Steve Muckle <smuckle@linaro.org>
Subject: Re: [PATCH 2/2] sched: cpufreq: use rt_avg as estimate of required RT CPU capacity
Date: Wed, 31 Aug 2016 16:39:07 +0200 [thread overview]
Message-ID: <20160831143907.GX10121@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1472236848-17038-3-git-send-email-smuckle@linaro.org>
On Fri, Aug 26, 2016 at 11:40:48AM -0700, Steve Muckle wrote:
> A policy of going to fmax on any RT activity will be detrimental
> for power on many platforms. Often RT accounts for only a small amount
> of CPU activity so sending the CPU frequency to fmax is overkill. Worse
> still, some platforms may not be able to even complete the CPU frequency
> change before the RT activity has already completed.
>
> Cpufreq governors have not treated RT activity this way in the past so
> it is not part of the expected semantics of the RT scheduling class. The
> DL class offers guarantees about task completion and could be used for
> this purpose.
Not entirely true. People have simply disabled cpufreq because of this.
Yes, RR/FIFO are a pain, but they should still be deterministic, and
variable cpufreq destroys that.
I realize that the fmax thing is annoying, but I'm not seeing how rt_avg
is much better.
next prev parent reply other threads:[~2016-08-31 14:39 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-26 18:40 [PATCH 0/2] utilization changes for schedutil Steve Muckle
2016-08-26 18:40 ` [PATCH 1/2] sched: cpufreq: ignore SMT when determining max cpu capacity Steve Muckle
2016-08-31 1:27 ` Rafael J. Wysocki
2016-08-31 14:34 ` Peter Zijlstra
2016-09-12 22:25 ` Rafael J. Wysocki
2016-08-26 18:40 ` [PATCH 2/2] sched: cpufreq: use rt_avg as estimate of required RT CPU capacity Steve Muckle
2016-08-31 1:31 ` Rafael J. Wysocki
2016-08-31 14:49 ` Steve Muckle
2016-08-31 14:39 ` Peter Zijlstra [this message]
2016-08-31 15:08 ` Steve Muckle
2016-08-31 16:28 ` Thomas Gleixner
2016-08-31 16:40 ` Peter Zijlstra
2016-08-31 17:00 ` Juri Lelli
2016-09-01 7:12 ` Peter Zijlstra
2016-09-01 21:48 ` Steve Muckle
2016-09-02 9:35 ` Juri Lelli
2016-09-02 12:17 ` Thomas Gleixner
2016-08-31 22:50 ` Rafael J. Wysocki
2016-09-02 8:12 ` Thomas Gleixner
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