linux-kernel - Re: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization update flags

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Date:   Mon, 18 Dec 2017 12:14:53 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization
 update flags

On 18-Dec 17:29, Viresh Kumar wrote:
> On 18-12-17, 12:35, Rafael J. Wysocki wrote:
> > Well, if SCHED_CPUFRREQ_CLEAR means "this CPU is going to enter the
> > idle loop" really, then it is better to call it
> > SCHED_CPUFRREQ_ENTER_IDLE, for example.
> > 
> > SCHED_CPUFRREQ_CLEAR meaning basically "you should clear these flags
> > now" doesn't seem to convey any information to whoever doesn't
> > squirrel the flags in the first place.
> 
> Right, but when all the flags are cleared, then we can infer that we
> are going to idle in the most probable case.
> 
> Anyway, I will implement RT and DL clear flags as you suggested in the
> next version.

I think Rafael is right, the current API is a big odd since we cannot
really set the CLEAR flags by itself. I mean, you can but it will not
have effects.

Thus, it's probably better from an API standpoint to have a dedicated
single clear flag... unfortunately it has to be one per class, which
is still not optimal and will likely make the policy code a bit odd.

What about extending the signature of the callback method?

For example, swithing from:

 - void (*func)(struct update_util_data *data, u64 time,
 -              unsigned int flags))
 + void (*func)(struct update_util_data *data, u64 time,
 +              unsigned int flags, bool set))

Where the additional boolean is actually used to define which
operation we wanna perform on the flags?

-- 
#include <best/regards.h>

Patrick Bellasi