Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs

From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux PM <linux-pm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Juri Lelli <juri.lelli@arm.com>,
	Patrick Bellasi <patrick.bellasi@arm.com>,
	Joel Fernandes <joelaf@google.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Ingo Molnar <mingo@redhat.com>
Subject: Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs
Date: Tue, 21 Mar 2017 15:58:08 +0100	[thread overview]
Message-ID: <20170321145808.GS3093@worktop> (raw)
In-Reply-To: <CAKfTPtALorn7HNpz4LOfWWSc3u+9y5iHB5byzfTHGQXDA+tVJQ@mail.gmail.com>

On Tue, Mar 21, 2017 at 03:16:19PM +0100, Vincent Guittot wrote:
> On 21 March 2017 at 15:03, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Tue, Mar 21, 2017 at 02:37:08PM +0100, Vincent Guittot wrote:
> > > On 21 March 2017 at 14:22, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > > For the not overloaded case, it makes sense to immediately update to
> > > OPP to be aligned with the new utilization of the CPU even if it was
> > > not idle in the past couple of ticks
> >
> > Yeah, but we cannot know. Also, who cares?
> >
> 
> embedded system that doesn't want to stay at higest OPP if significant part
> of the utilzation has moved away as an example
> AFAICT, schedutil tries to select the best OPP according to the current
> utilization of the CPU so if the utilization decreases, the OPP should also
> decrease

Sure I get that; but given the lack of crystal ball instructions we
cannot know if this is the case or not.

And if we really dropped below 100% utilization, we should hit idle
fairly soon.