On 4 June 2014 11:42, Dietmar Eggemann <dietmar.eggem...@arm.com> wrote: > [...] >>> (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 > > I think I mixed two problems together here: > > Firstly, we need to scale cpu power in update_cpu_power() regarding > uArch, frequency and rt/irq pressure. > Here the freq related value we get back from arch_scale_freq_power(..., > cpu) could be an instantaneous value (curr_freq(cpu)/max_freq(cpu)). > > Secondly, to be able to scale the runnable avg sum of a sched entity > (se->avg->runnable_avg_sum), we preferable have a coefficient > representing uArch diffs (cpu_power_orig(cpu)/cpu_power_orig(most > powerful cpu in the system) and another coefficient (avg freq over 'now
AFAICT, the coefficient representing uArch diffs is already taken into account into power_freq thanks to scale_cpu, isn't it ? > - sa->last_runnable_update'(cpu)/max_freq(cpu). This value would have to > be retrieved from the arch in __update_entity_runnable_avg(). > >>> (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) ? > > No, I also think that power=scale_rt(power_freq) is correct. > >>> 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 > [...] > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
