Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 17 Jan 2020 16:39:37 +0100 | Subject | Re: [Patch v8 4/7] sched/fair: Enable periodic update of average thermal pressure |
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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
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