linux-kernel - Re: [PATCH sched_ext/for-6.13 2/2] sched_ext: Enable the ops breather and eject BPF scheduler on softlockup

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Message-ID: <Zyv2x6kb3gO8cTO7@slm.duckdns.org>
Date: Wed, 6 Nov 2024 13:07:51 -1000
From: Tejun Heo <tj@...nel.org>
To: Doug Anderson <dianders@...omium.org>
Cc: David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, sched-ext@...a.com,
	Andrea Righi <arighi@...dia.com>,
	Changwoo Min <multics69@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH sched_ext/for-6.13 2/2] sched_ext: Enable the ops
 breather and eject BPF scheduler on softlockup

Hello,

On Wed, Nov 06, 2024 at 03:02:35PM -0800, Doug Anderson wrote:
...
> Honestly, it would feel better to me if the soft lockup timer didn't
> tell schedext to kill things but instead we just make some special
> exception for "schedext" tasks and exclude them from the softlockup
> detector because they're already being watched by their own watchdog.
> Would that be possible? Then tweaking the "softlockup" timeouts
> doesn't implicitly change how long schedext things can run.

Some systems can get into full blown live-lock condition where CPUs are
barely making forward progress through the scheduler and all normal (!RT &&
!DEADLINE) tasks are on sched_ext, so the only reasonable way to exclude
sched_ext would be disabling softlockup detection while sched_ext is
enabled which doesn't feel like a sound trade-off.

Thanks.

-- 
tejun