Re: [PATCH V2] sched/fair: Dequeue sched_delayed tasks when waking to a busy CPU

Phil Auld
2024-12-09T13:11:25Z

Hi Mike et al.,

On Mon, Dec 02, 2024 at 02:12:52PM -0500 Phil Auld wrote:
> On Mon, Dec 02, 2024 at 05:55:28PM +0100 Mike Galbraith wrote:
> > On Mon, 2024-12-02 at 11:24 -0500, Phil Auld wrote:
> > > On Sat, Nov 23, 2024 at 09:44:40AM +0100 Mike Galbraith wrote:
> > >
> > >
> > > > Question: did wiping off the evil leave any meaningful goodness behind?
> > >
> > > Is that for this patch?
> >
> > Yeah. Trying it on my box with your write command line didn't improve
> > the confidence level either. My box has one CPU handling IRQs and
> > waking pinned workers to service 8 fio instances. Patch was useless
> > for that.
> >
>
> I'll give it a try. Our "box" is multiple different boxes but the results
> vary somewhat. The one I sent info about earlier in this thread is just
> one of the more egregious and is the one the perf team lent me for a while.
>

In our testing this has the same effect as the original dequeue-when-delayed
fix. It solves the randwrite issue and introduces the ~10-15% randread
regression.

Seems to be a real trade-off here. The same guys who benefit from spreading
in one case benefit from staying put in the other...

Cheers,
Phil

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