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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241209131110.GC117639@pauld.westford.csb>
Date: Mon, 9 Dec 2024 08:11:10 -0500
From: Phil Auld <pauld@...hat.com>
To: Mike Galbraith <efault@....de>
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


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

--