Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 30 May 2014 22:50:20 +0200 | Subject | Re: [PATCH v2 04/11] sched: Allow all archs to set the power_orig |
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On 30 May 2014 16:04, Dietmar Eggemann <dietmar.eggemann@arm.com> 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?
Using power (or power_freq as you mentioned below) is probably the easiest and more straight forward solution. You can use it to scale each element when updating entity runnable. Nevertheless, I see to 2 potential issues: - is power updated often enough to correctly follow the frequency scaling ? we need to compare power update frequency with runnable_avg_sum variation speed and the rate at which we will change the CPU's frequency. - the max value of runnable_avg_sum will be also scaled so a task running on a CPU with less capacity could be seen as a "low" load even if it's an always running tasks. So we need to find a way to reach the max value for such situation
> > (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))
do you really mean power = scale_rt(power_orig) or power=scale_rt(power_freq) ?
> > In other words, do we consider rt/(irq) pressure when calculating freq > scale invariant task load or not?
we should take power_freq which implies a new field
Thanks, Vincent > > Thanks, > > -- Dietmar > [...] >
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