linux-kernel - Re: [RFC v2 1/8] sched/tune: add detailed documentation

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Message-ID: <20161104094642.GF3414@vireshk-i7>
Date:   Fri, 4 Nov 2016 15:16:42 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steve Muckle <steve.muckle@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Todd Kjos <tkjos@...gle.com>,
        Srinath Sridharan <srinathsr@...gle.com>,
        Andres Oportus <andresoportus@...gle.com>,
        Juri Lelli <juri.lelli@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Chris Redpath <chris.redpath@....com>,
        Robin Randhawa <robin.randhawa@....com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [RFC v2 1/8] sched/tune: add detailed documentation

On 27-10-16, 18:41, Patrick Bellasi wrote:
> +This last requirement is especially important if we consider that schedutil can
> +potentially replace all currently available CPUFreq policies. Since schedutil
> +is event based, as opposed to the sampling driven governors, it is already more
> +responsive at selecting the optimal OPP to run tasks allocated to a CPU.

I am not sure if I follow this paragraph. All the governors follow the same
basic rules now. They are all event driven (events from scheduler), but they
function only after a certain sampling period is finished. Isn't this the case ?

> +SchedTune exposes a simple user-space interface with a single power-performance
> +tunable:
> +
> +  /proc/sys/kernel/sched_cfs_boost
> +
> +This permits expressing a boost value as an integer in the range [0..100].
> +
> +A value of 0 (default) for a CFS task means that schedutil will attempt
> +to match compute capacity of the CPU where the task is scheduled to
> +match its current utilization with a few spare cycles left. A value of
> +100 means that schedutil will select the highest available OPP.
> +
> +The range between 0 and 100 can be set to satisfy other scenarios suitably.
> +For example to satisfy interactive response or depending on other system events
> +(battery level, thermal status, etc).

Earlier section said that schedutil+schedtune can replace all earlier governors.
How will schedutil behave like powersave governor with schedtune? I was
expecting the possible values of sched_cfs_boost to be in the range -100 to 100,
where -100 will make it powersave, +100 will make it performance and 0 will not
make any changes.

-- 
viresh