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    SubjectRe: [PATCH v5 11/12] sched: replace capacity_factor by utilization
    On Tue, Sep 16, 2014 at 12:14:54AM +0200, Vincent Guittot wrote:
    > On 15 September 2014 13:42, Peter Zijlstra <peterz@infradead.org> wrote:

    > > OK, I've reconsidered _again_, I still don't get it.
    > >
    > > So fundamentally I think its wrong to scale with the capacity; it just
    > > doesn't make any sense. Consider big.little stuff, their CPUs are
    > > inherently asymmetric in capacity, but that doesn't matter one whit for
    > > utilization numbers. If a core is fully consumed its fully consumed, no
    > > matter how much work it can or can not do.
    > >
    > >
    > > So the only thing that needs correcting is the fact that these
    > > statistics are based on clock_task and some of that time can end up in
    > > other scheduling classes, at which point we'll never get 100% even
    > > though we're 'saturated'. But correcting for that using capacity doesn't
    > > 'work'.
    >
    > I'm not sure to catch your last point because the capacity is the only
    > figures that take into account the "time" consumed by other classes.
    > Have you got in mind another way to take into account the other
    > classes ?

    So that was the entire point of stuffing capacity in? Note that that
    point was not at all clear.

    This is very much like 'all we have is a hammer, and therefore
    everything is a nail'. The rt fraction is a 'small' part of what the
    capacity is.

    > So we have cpu_capacity that is the capacity that can be currently
    > used by cfs class
    > We have cfs.usage_load_avg that is the sum of running time of cfs
    > tasks on the CPU and reflect the % of usage of this CPU by CFS tasks
    > We have to use the same metrics to compare available capacity for CFS
    > and current cfs usage

    -ENOPARSE

    > Now we have to use the same unit so we can either weight the
    > cpu_capacity_orig with the cfs.usage_load_avg and compare it with
    > cpu_capacity
    > or with divide cpu_capacity by cpu_capacity_orig and scale it into the
    > SCHED_LOAD_SCALE range. Is It what you are proposing ?

    I'm so not getting it; orig vs capacity still includes
    arch_scale_freq_capacity(), so that is not enough to isolate the rt
    fraction.


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