Re: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization update flags

From: Peter Zijlstra
Date: Wed Dec 20 2017 - 08:28:37 EST

On Wed, Dec 20, 2017 at 12:55:46PM +0000, Patrick Bellasi wrote:
> On 20-Dec 09:31, Peter Zijlstra wrote:

> > Didn't juri have patches to make DL do something sane? But yes, I think
> > those flags are part of the problem.
> He recently reposted them here:

Yeah, just found them and actually munged them into my queue; did all
the modifications you suggested too. Lets see if it comes apart.

> > > - From the utilization handler, we check runqueues of all three sched
> > > classes to see if they have some work pending (this can be done
> > > smartly by checking only RT first and skipping other checks if RT
> > > has some work).
> >
> > No that's wrong. DL should provide a minimum required based on existing
> > reservations, we can add the expected CFS average on top and request
> > that.
> >
> > And for RT all we need to know is if current is of that class, otherwise
> > we don't care.
> So, this:

Right, I was actually looking for those patches, but I'm searching
backwards and hit upon Juri's patches first.

> was actually going in this direction, although still working on top of
> flags to not change the existing interface too much.
> IMO, the advantage of flags is that they are a sort-of "pro-active"
> approach, where the scheduler notify sensible events to schedutil.
> But keep adding flags seems to overkilling to me too.
> If we remove flags then we have to query the scheduler classes "on
> demand"... but, as Peter suggests, once we have DL bits Juri posted,
> the only issue if to know if an RT task is running.
> This the patch above can be just good enough, with no flags at all and
> with just a check for current being RT (or DL for the time being).

Well, we still need flags for crap like IO-WAIT IIRC. That's sugov
internal state and not something the scheduler actually already knows.

But let me continue searching for patches..

Ooh, I found patches from Brendan... should be very close to yours
though, going by that msgid you posted on Nov 30th and I'm now on Dec
1st, soooon... :-)