Re: [Patch v8 4/7] sched/fair: Enable periodic update of average thermal pressure

[Peter Zijlstra]

On Fri, Jan 17, 2020 at 02:22:51PM +0100, Vincent Guittot wrote:
> On Thu, 16 Jan 2020 at 16:15, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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?

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.