linux-kernel - Re: [PATCH v6 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil

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Date:   Fri, 07 Sep 2018 10:52:01 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Quentin Perret <quentin.perret@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Chris Redpath <chris.redpath@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Steve Muckle <smuckle@...gle.com>, adharmap@...eaurora.org,
        Saravana Kannan <skannan@...eaurora.org>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        currojerez@...eup.net, Javi Merino <javi.merino@...nel.org>
Subject: Re: [PATCH v6 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil

On Thursday, September 6, 2018 4:38:44 PM CEST Quentin Perret wrote:
> Hi Rafael,
> 
> On Thursday 06 Sep 2018 at 11:18:55 (+0200), Rafael J. Wysocki wrote:
> > I'm not a particular fan of notifiers to be honest and you don't need
> > to add an extra chain just in order to be able to register a callback
> > from a single user.
> 
> Right. I agree there are alternatives to using notifiers. I used them
> because they're existing infrastructure, and because they let me do what
> I want without too much troubles, which are two important points.
> 
> > That can be achieved with a single callback
> > pointer too, but also you could just call a function exported by the
> > scheduler directly from where in the cpufreq code it needs to be
> > called.
> 
> Are you thinking about something comparable to what is done in
> cpufreq_add_update_util_hook() (kernel/sched/cpufreq.c) for example ?
> That would probably have the same drawback as my current implementation,
> that is that the scheduler is notified of _all_ governor changes, not
> only changes to/from sugov although this is the only thing we care about
> for EAS.

Well, why don't you implement it as something like "if the governor changes
from sugov to something else (or the other way around), call this function
from the scheduler"?