Messages in this thread | | | Subject | Re: [Patch v8 4/7] sched/fair: Enable periodic update of average thermal pressure | From | Dietmar Eggemann <> | Date | Fri, 24 Jan 2020 16:37:23 +0100 |
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On 17/01/2020 16:39, Vincent Guittot wrote: > On Fri, 17 Jan 2020 at 15:55, Peter Zijlstra <peterz@infradead.org> wrote: >> >> On Fri, Jan 17, 2020 at 02:22:51PM +0100, Vincent Guittot wrote: >>> On Thu, 16 Jan 2020 at 16:15, Peter Zijlstra <peterz@infradead.org> wrote: >> >>>> >>>> That there indentation trainwreck is a reason to rename the function. >>>> >>>> decayed = update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) | >>>> update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) | >>>> update_thermal_load_avg(rq_clock_task(rq), rq, thermal_pressure) | >>>> update_irq_load_avg(rq, 0); >>>> >>>> Is much better. >>>> >>>> But now that you made me look at that, I noticed it's using a different >>>> clock -- it is _NOT_ using now/rq_clock_pelt(), which means it'll not be >>>> in sync with the other averages. >>>> >>>> Is there a good reason for that? >>> >>> We don't need to apply frequency and cpu capacity invariance on the >>> thermal capping signal which is what rq_clock_pelt does >> >> Hmm, I suppose that is true, and that really could've done with a >> comment. Now clock_pelt is sort-of in sync with clock_task, but won't it >> still give weird artifacts by having it on a slightly different basis? > > No we should not. Weird artifacts happens when we > add/subtract/propagate signals between each other and then apply pelt > algorithm on the results. In the case of thermal signal, we only add > it to others to update cpu_capacity but pelt algo is then not applied > on it. The error because of some signals being at segment boundaries > whereas others are not, is limited to 2% and doesn't accumulate over > time. > >> >> Anyway, looking at this, would it make sense to remove the @now argument >> from update_*_load_avg()? All those functions already take @rq, and >> rq_clock_*() are fairly trivial inlines. > > TBH I was thinking of doing the opposite for update_irq_load_avg which > hides the clock that is used for irq_avg. This helps to easily > identify which signals use the exact same clock and can be mixed to > create a new pelt signal and which can't
The 'now' argument is one thing but why not:
-int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity) +int update_thermal_load_avg(u64 now, struct rq *rq) { + u64 capacity = arch_cpu_thermal_pressure(cpu_of(rq)); + if (___update_load_sum(now, &rq->avg_thermal,
This would make the call-sites __update_blocked_others() and task_tick(_fair)() cleaner.
I guess the argument is not to pollute pelt.c. But it already contains arch_scale_[freq|cpu]_capacity() for irq.
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