linux-kernel - Re: [PATCH v2 05/10] um: Determine sleep based on need

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Message-Id: <20250911043918.2950727-1-tiwei.bie@linux.dev>
Date: Thu, 11 Sep 2025 12:39:18 +0800
From: Tiwei Bie <tiwei.bie@...ux.dev>
To: johannes@...solutions.net
Cc: richard@....at,
	anton.ivanov@...bridgegreys.com,
	benjamin@...solutions.net,
	arnd@...db.de,
	linux-um@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	tiwei.btw@...group.com,
	tiwei.bie@...ux.dev
Subject: Re: [PATCH v2 05/10] um: Determine sleep based on need_resched()

On Wed, 10 Sep 2025 14:10:37 +0200, Johannes Berg wrote:
> On Sun, 2025-08-10 at 13:51 +0800, Tiwei Bie wrote:
> > From: Tiwei Bie <tiwei.btw@...group.com>
> > 
> > With SMP and NO_HZ enabled, the CPU may still need to sleep even
> > if the timer is disarmed. Switch to deciding whether to sleep based
> > on pending resched. This is a preparation for adding SMP support.
> 
> What's the rationale for need_resched()? Is that somehow defined for
> this? Is it what other architectures use? I guess I'm just not entirely
> sure what it means.

Here is a relevant document:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/scheduler/sched-arch.rst?h=v6.17-rc5#n37

There is a similar check on x86:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/process.c?h=v6.17-rc5#n916

Regards,
Tiwei