linux-kernel - Re: [PATCH v1 4/7] sched/isolation: Adjust affinity of managed irqs according to change of housekeeping cpumask

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Date: Mon, 27 May 2024 15:21:50 +0300
From: Costa Shulyupin <costa.shul@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: longman@...hat.com, pauld@...hat.com, linux-kernel@...r.kernel.org, 
	Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH v1 4/7] sched/isolation: Adjust affinity of managed irqs
 according to change of housekeeping cpumask

Hello Thomas,

Thank you so much for very valuable feedback!
I've tested your proposal to use the hotplug for the isolation.
It works well for both timers, but managed irqs are not ready for this scenario.

Current implementation is introduced by
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=11ea68f553e244851d15793a7fa33a97c46d8271

How do you suggest to proceed?

> So why inflicting all of this nonsense to the kernel instead of
> cleverly (ab)using CPU hotplug for it in user space:
..


> Or something like that. You get the idea, right?
>
> IOW, the only kernel change which is required to achieve your goal is to
> ensure that changing the housekeeping/isolated property of a CPU at
> runtime is only possible when the CPU is "offline".