Re: [PATCH v6 07/16] sched/core: uclamp: Add system default clamps

Peter Zijlstra
2019-01-23T19:10:07Z

On Wed, Jan 23, 2019 at 02:19:24PM +0000, Patrick Bellasi wrote:
> On 23-Jan 10:22, Peter Zijlstra wrote:
> > On Tue, Jan 22, 2019 at 03:41:29PM +0000, Patrick Bellasi wrote:
> > > On 22-Jan 16:13, Peter Zijlstra wrote:
> > > > On Tue, Jan 22, 2019 at 02:43:29PM +0000, Patrick Bellasi wrote:
> >
> > > > > Do you think that could be acceptable?
> > > >
> > > > Think so, it's a sysctl poke, 'nobody' ever does that.
> > >
> > > Cool, so... I'll keep lazy update for system default.
> >
> > Ah, I think I misunderstood. I meant to say that since nobody ever pokes
> > at sysctl's it doesn't matter if its a little more expensive and iterate
> > everything.
>
> Here I was more worried about the code complexity/overhead... for
> something actually not very used/useful.
>
> > Also; if you always keep everything up-to-date, you can avoid doing that
> > duplicate accounting.
>
> To update everything we will have to walk all the CPUs and update all
> the RUNNABLE tasks currently enqueued, which are either RT or CFS.
>
> That's way more expensive both in code and time then what we do for
> cgroups, where at least we have a limited scope since the cgroup
> already provides a (usually limited) list of tasks to consider.
>
> Do you think it's really worth to have ?

Dunno; the whole double bucket thing seems a bit weird to me; but maybe
it will all look better without the mapping stuff.