Date: Tue, 21 Mar 2017 15:03:25 +0100
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
Message-ID: <20170321140325.gf64gc7eaqu335t5@hirez.programming.kicks-ass.net>
References: <4366682.tsferJN35u@aspire.rjw.lan>
 <2185243.flNrap3qq1@aspire.rjw.lan>
 <3300960.HE4b3sK4dn@aspire.rjw.lan>
 <CAKfTPtB0WpvSz66UNK5HNQF8W-PKCYNyRSCzz9L9WRAKNy+KYw@mail.gmail.com>
 <20170321132253.vjp7f72qkubpttmf@hirez.programming.kicks-ass.net>
 <CAKfTPtBp7GevDfnOTrOnrc79XP1mbY0onq=uh4Aw2tGu-DgHGw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKfTPtBp7GevDfnOTrOnrc79XP1mbY0onq=uh4Aw2tGu-DgHGw@mail.gmail.com>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 927
Lines: 23

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?

> > does exactly that. Note that the lack of idle time is an exact
> > equivalent of 100% utilized.
> >
> > So even while we cannot currently detect the 100% utilized state through
> > the running state tracking; because averages etc.. we can detect the
> > lack of idle time.
> 
> But after how much lack of idle time do we consider that we are overloaded ?

0 :-)

Note that utilization is an absolute metric, not a windowed one. That
is, there is no actual time associated with it. Now, for practical
purposes we end up using windowed things in many places,