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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Wed, 3 Jun 2020 21:24:56 +0200
Message-ID: <CAKfTPtBdN30ChMgFqqT1bzeU6HExXEQFrQjxbCK-hRT4HEiQkQ@mail.gmail.com>
Subject: Re: v5.7: new core kernel option missing help text
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc:     Valentin Schneider <valentin.schneider@arm.com>,
        Thara Gopinath <thara.gopinath@linaro.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Wed, 3 Jun 2020 at 20:45, Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
>
> On Wed, Jun 03, 2020 at 07:00:26PM +0100, Valentin Schneider wrote:
> >
> > On 03/06/20 18:31, Russell King - ARM Linux admin wrote:
> > > Hi,
> > >
> > > A new kernel configuration option ("SCHED_THERMAL_PRESSURE") was
> > > recently added, but has no help text. This is most unhelpful when
> > > trying to configure the kernel, since one does not know what the
> > > effect of answering yes or no to this option would be.
> > >
> > > Please supply a proper help text when adding core kernel options
> > > so that people can make an informed decision when answering the
> > > prompt, rather than just guessing.
> > >
> >
> > Right; does the below look good enough?
>
> It's a start.  I'm still wondering whether I should answer yes or no
> for the platforms I'm building for.
>
> So far, all I've found is:
>
> arch/arm/include/asm/topology.h:#define arch_scale_thermal_pressure topology_get_thermal_pressure
>
> which really doesn't tell me anything about this.  So I'm still in
> the dark.
>
> I guess topology_get_thermal_pressure is provided by something in
> drivers/ which will be conditional on some driver or something.

You need cpufreq_cooling device to make it useful and only for SMP
I don't think that this should not be user configurable because even
with the description above, it is not easy to choose.
This should be set by the driver that implement the feature which is
only cpufreq cooling device for now it

>
> >
> > ---
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 74a5ac65644f..f40cf852d00a 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -441,6 +441,10 @@ config HAVE_SCHED_AVG_IRQ
> >  config SCHED_THERMAL_PRESSURE
> >         bool "Enable periodic averaging of thermal pressure"
> >         depends on SMP
> > +     help
> > +       This option allows the scheduler to be aware of CPU thermal throttling
> > +       (i.e. thermal pressure), providing arch_scale_thermal_pressure() is
> > +       implemented.
> >
> >  config BSD_PROCESS_ACCT
> >         bool "BSD Process Accounting"
> > ---
> >
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC for 0.8m (est. 1762m) line in suburbia: sync at 13.1Mbps down 424kbps up