Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20180724122521.22109-1-quentin.perret@arm.com>
 <20180724122521.22109-10-quentin.perret@arm.com> <20180802122629.GU2476@hirez.programming.kicks-ass.net>
 <20180802130337.uf6tlac2hg4nkbwr@queper01-lin> <20180802130801.GL2494@hirez.programming.kicks-ass.net>
 <20180802131849.mqpt5lbtcqrxbwig@queper01-lin> <CAKfTPtDcoySXK0fBkDNy4wp1vsRxmiuAGT3CDZBh6Vnwyep2BA@mail.gmail.com>
 <20180802141424.ju4jxxbk6pxw3kyq@queper01-lin> <CAKfTPtCzQZotmpt40X6uN9O0yAerq6c6bFgiFfqhhcbKsm7k4w@mail.gmail.com>
 <20180802153035.vjtmqwdwujvt7ojs@queper01-lin>
In-Reply-To: <20180802153035.vjtmqwdwujvt7ojs@queper01-lin>
From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Thu, 2 Aug 2018 17:55:24 +0200
Message-ID: <CAKfTPtCGGqykN027kxK+chvKvCpNu4bYYdvfZJ+3_7YzT3Utfg@mail.gmail.com>
Subject: Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator
To:     Quentin Perret <quentin.perret@arm.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "open list:THERMAL" <linux-pm@vger.kernel.org>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Chris Redpath <chris.redpath@arm.com>,
        Patrick Bellasi <patrick.bellasi@arm.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Thara Gopinath <thara.gopinath@linaro.org>,
        viresh kumar <viresh.kumar@linaro.org>,
        Todd Kjos <tkjos@google.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        "Cc: Steve Muckle" <smuckle@google.com>, adharmap@quicinc.com,
        "Kannan, Saravana" <skannan@quicinc.com>, pkondeti@codeaurora.org,
        Juri Lelli <juri.lelli@redhat.com>,
        Eduardo Valentin <edubezval@gmail.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        currojerez@riseup.net, Javi Merino <javi.merino@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, 2 Aug 2018 at 17:30, Quentin Perret <quentin.perret@arm.com> wrote:
>
> On Thursday 02 Aug 2018 at 17:14:15 (+0200), Vincent Guittot wrote:
> > On Thu, 2 Aug 2018 at 16:14, Quentin Perret <quentin.perret@arm.com> wrote:
> > > Good point, setting the util_avg to 0 for new tasks should help
> > > filtering out those tiny tasks too. And that would match with the idea
> > > of letting tasks build their history before looking at their util_avg ...
> > >
> > > But there is one difference w.r.t frequency selection. The current code
> > > won't mark the system overutilized, but will let sugov raise the
> > > frequency when a new task is enqueued. So in case of a fork bomb, we
> >
> > If the initial value of util_avg is 0, we should not have any impact
> > on the util_avg of the cfs rq on which the task is attached, isn't it
> > ? so this should not impact both the over utilization state and the
> > frequency selected by sugov or I'm missing something ?
>
> What I tried to say is that setting util_avg to 0 for new tasks will
> prevent schedutil from raising the frequency in case of a fork bomb, and
> I think that could be an issue. And I think this isn't an issue with the
> patch as-is ...

ok. So you also want to deal with fork bomb
Not sure that you don't have some problem with current proposal too
because select_task_rq_fair will always return prev_cpu because
util_avg and util_est are 0 at that time

>
> Sorry if that wasn't clear
>
> > Then, select_task_rq_fair is called for a new task but util_avg is
> > still 0 at that time in the current code so you will have consistent
> > util_avg of the new task before and after calling
> > find_energy_efficient_cpu
>
> New tasks don't go in find_energy_efficient_cpu(), because, as you said,
> they have no consistent util_avg yet when select_task_rq_fair() is called
> for the first time.
>
> Thanks,
> Quentin