linux-kernel - Re: [PATCH sched_ext/for-6.13 1/2] sched_ext: Avoid live-locking bypass mode switching

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Message-ID: <Zyq3vmLP4R2WjnmB@slm.duckdns.org>
Date: Tue, 5 Nov 2024 14:26:38 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, sched-ext@...a.com,
	Changwoo Min <multics69@...il.com>
Subject: Re: [PATCH sched_ext/for-6.13 1/2] sched_ext: Avoid live-locking
 bypass mode switching

Hello,

On Wed, Nov 06, 2024 at 12:57:42AM +0100, Andrea Righi wrote:
...
> Do you think there's any benefit using the idle injection framework here
> instead of this cpu_relax() loop? At the end we're trying to throttle
> the scx scheduler from hammering a DSQ until the scheduler is kicked
> out, so we may just inject real idle cycles?

That involves switching to the dedicated task and so on, right? When this is
needed, we can't even trust whether the system is going to make forward
progress within the scheduler. I don't think it'd be a good idea to call out
to something more complicated. Also, from forward-progress-guaranteeing
point of view, cpu_relax() is as good as anything else and this shouldn't be
active long enough for power consumption to be a factor.

Thanks.

-- 
tejun