[...] >> (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 - 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/
