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    SubjectRe: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable
    On 16/03/16 10:55, Steve Muckle wrote:
    > On 03/16/2016 03:02 AM, Juri Lelli wrote:
    > > Hi,
    > >
    > > On 16/03/16 09:05, Peter Zijlstra wrote:
    > >> On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
    > >>>> Then again, maybe this knob will be part of the mythical
    > >>>> power-vs-performance slider?
    > >>>
    > >>> Patrick Bellasi's schedtune series [0] (which I think is the referenced
    > >>> mythical slider) aims to provide a more sophisticated interface for
    > >>> tuning scheduler-driven frequency selection. In addition to a global
    > >>> boost value it includes a cgroup controller as well for per-task tuning.
    > >>>
    > >>> I would definitely expect the margin/boost value to be modified at
    > >>> runtime, for example if the battery is running low, or the user wants
    > >>> 100% performance for a while, or the userspace framework wants to
    > >>> temporarily tailor the performance level for a particular set of tasks, etc.
    > >>
    > >> OK, so how about we start with it as a debug knob, and once we have
    > >> experience and feel like it is indeed a useful runtime knob, we upgrade
    > >> it to ABI.
    > >>
    > >
    > > I tend to agree here. To me the margin is something that we need to make
    > > this thing work and to get acceptable performance out of the box. So we
    > > can play with it while debugging, but I consider the schedtune slider as
    > > the way to tune the system at runtime.
    >
    > Could the default schedtune value not serve as the out of the box margin?
    >

    I'm not sure I understand you here. For me schedtune should be disabled
    by default, so I'd say that it doesn't introduce any additional margin
    by default. But we still need a margin to make the governor work without
    schedtune in the mix.

    > Regardless I agree that a debug interface is the way to go for now while
    > we figure things out.
    >

    Looks good to me.

    Best,

    - Juri

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