Re: [RFC PATCH 8/8] arm64: add sysfs cpu_capacity attribute

From	Mark Brown <broonie@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 8/8] arm64: add sysfs cpu_capacity attribute
Date	2015-12-11 19:00 +0100
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On Thu, Dec 10, 2015 at 06:01:59PM +0000, Juri Lelli wrote:
> On 10/12/15 15:59, Mark Brown wrote:
> > On Thu, Dec 10, 2015 at 02:15:04PM +0000, Dietmar Eggemann wrote:
> > > On 23/11/15 14:28, Juri Lelli wrote:

> > > > The new attribute shows up as:

> > > >  /sys/devices/system/cpu/cpu*/cpu_capacity

> > > This sysfs interface is not really needed for arm or arm64. People can
> > > build the dt blob if they want to change the values. Less code to carry
> > > ... Let's focus on the core functionality, which is parsing cpu capacity
> > > from dt file to task scheduler for heterogeneous systems.

> > That does make the tuning process much more cumbersome - users have to
> > rebuild and reboot to tweak the numbers rather than just tweaking the
> > numbers and rerunning the benchmark (which seems like something people
> > would want to automate).

> IMHO, this is not a tuning interface. It is an alternative interface,
> w.r.t. DTs, that we could use to provide default capacity values to the
> kernel. I'm proposing both here as they make both sense to me. Then we
> might dedice for which one to go (or if we need some other way) or to
> keep both for flexibility.

Kind of repeating what I said in the other mail but I'd say that any
interface which provides a mechanism for setting a magic number that
influences system performance is providing tuning.  It's hard to see how
else to describe it to be honest.

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Re: [RFC PATCH 8/8] arm64: add sysfs cpu_capacity attribute Dietmar Eggemann <dietmar.eggemann@arm.com> - 2015-12-10 15:20 +0100
  Re: [RFC PATCH 8/8] arm64: add sysfs cpu_capacity attribute Mark Brown <broonie@kernel.org> - 2015-12-10 17:00 +0100
    Re: [RFC PATCH 8/8] arm64: add sysfs cpu_capacity attribute Juri Lelli <juri.lelli@arm.com> - 2015-12-10 19:10 +0100
      Re: [RFC PATCH 8/8] arm64: add sysfs cpu_capacity attribute Mark Brown <broonie@kernel.org> - 2015-12-11 19:00 +0100

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