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

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Message-ID: <b5239b5fd2680c4cef61d526a44fdb5a37c256b8.camel@gmx.de>
Date: Mon, 09 Dec 2024 16:06:48 +0100
From: Mike Galbraith <efault@....de>
To: Phil Auld <pauld@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com, 
 juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com,  rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com,  linux-kernel@...r.kernel.org,
 kprateek.nayak@....com, wuyun.abel@...edance.com, 
 youssefesmat@...omium.org, tglx@...utronix.de
Subject: Re: [PATCH V2] sched/fair: Dequeue sched_delayed tasks when waking
 to a busy CPU

On Mon, 2024-12-09 at 08:11 -0500, Phil Auld wrote:
>
> 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...

Does as much harm as it does good isn't the mark of a keeper.  Oh well.

	-Mike