Re: [RFC PATCH v7] sched/fair: select idle cpu from idle cpumask for task wakeup

Peter Zijlstra
2020-12-14T09:33:54Z

On Fri, Dec 11, 2020 at 10:50:02PM +0000, Mel Gorman wrote:

> > > The third potential downside is that the SMT sibling is not guaranteed to
> > > be checked due to SIS_PROP throttling but in the old code, that would have
> > > been checked by select_idle_smt(). That might result in premature stacking
> > > of runnable tasks on the same CPU. Similarly, as __select_idle_core may
> > > find multiple idle candidates, it will not pick the targets SMT sibling
> > > if it is idle like select_idle_smt would have.
> > >
> > > That said, I am skeptical that select_idle_smt() matters all that often.
> >
> > This, I didn't really believe in it either.
> >
>
> Good because I think any benefit from select_idle_smt is so marginal
> that it should be ignored if the full scan is simpler overall.

Perhaps we should start out with a simple patch removing that pass..
That should show, what, if anything, the effect of it is.