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    SubjectRe: [PATCH v2 04/11] sched: Allow all archs to set the power_orig
    On Fri, May 30, 2014 at 03:04:32PM +0100, Dietmar Eggemann wrote:
    > On 23/05/14 16:52, Vincent Guittot wrote:
    > > power_orig is only changed for system with a SMT sched_domain level in order to
    > > reflect the lower capacity of CPUs. Heterogenous system also have to reflect an
    > > original capacity that is different from the default value.
    > >
    > > Create a more generic function arch_scale_cpu_power that can be also used by
    > > non SMT platform to set power_orig.
    > >
    > > The weak behavior of arch_scale_cpu_power is the previous SMT one in order to
    > > keep backward compatibility in the use of power_orig.
    > >
    > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
    >
    > As you know, besides uarch scaled cpu power for HMP, freq scaled cpu
    > power is important for energy-aware scheduling to achieve freq scale
    > invariance for task load.
    >
    > I know that your patch-set is not about introducing freq scaled cpu
    > power, but we were discussing how this can be achieved w/ your patch-set
    > in place, so maybe you can share your opinion regarding the easiest way
    > to achieve freq scale invariance with us?
    >
    > (1) We assume that the current way (update_cpu_power() calls
    > arch_scale_freq_power() to get the avg power(freq) over the time period
    > since the last call to arch_scale_freq_power()) is suitable
    > for us. Do you have another opinion here?
    >
    > (2) Is the current layout of update_cpu_power() adequate for this, where
    > we scale power_orig related to freq and then related to rt/(irq):
    >
    > power_orig = scale_cpu(SCHED_POWER_SCALE)
    > power = scale_rt(scale_freq(power_orig))
    >
    > or do we need an extra power_freq data member on the rq and do:
    >
    > power_orig = scale_cpu(SCHED_POWER_SCALE)
    > power_freq = scale_freq(power_orig))
    > power = scale_rt(power_orig))
    >
    > In other words, do we consider rt/(irq) pressure when calculating freq
    > scale invariant task load or not?

    I don't think you should. The work done depends on the frequency, not on
    other tasks present on the cpu. The same is true for an over-utilized
    cpu, a task will run less than the desired amount of time, this is no
    different from a RT/irq preempting the task and taking its time.
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