linux-kernel - Re: [PATCH 2/3] rcu: Defer RCU kthreads wakeup when CPU is dying

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Message-ID: <29781c9b46641e3cbcd9d3874cb18f90ea916193.camel@mediatek.com>
Date: Mon, 12 Aug 2024 11:53:15 +0000
From: Cheng-Jui Wang (王正睿)
	<Cheng-Jui.Wang@...iatek.com>
To: "frederic@...nel.org" <frederic@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peterz@...radead.org" <peterz@...radead.org>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "qiang.zhang1211@...il.com"
	<qiang.zhang1211@...il.com>, "paulmck@...nel.org" <paulmck@...nel.org>,
	"neeraj.upadhyay@....com" <neeraj.upadhyay@....com>,
	Bobule Chang (張弘義) <bobule.chang@...iatek.com>,
	"boqun.feng@...il.com" <boqun.feng@...il.com>, "urezki@...il.com"
	<urezki@...il.com>, "joel@...lfernandes.org" <joel@...lfernandes.org>,
	"rcu@...r.kernel.org" <rcu@...r.kernel.org>
Subject: Re: [PATCH 2/3] rcu: Defer RCU kthreads wakeup when CPU is dying

On Mon, 2024-08-12 at 13:13 +0200, Frederic Weisbecker wrote:
> 
> This means you are setting rcuo kthreads as real time
> tasks. I would be curious about your usecase.

I think it might simply be that CONFIG_RCU_BOOST=y was enabled. This
causes kthread_prio to be set to 1.

	static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;

Then, when creating rcuog kthread, since kthread_prio is 1, it will
automatically set it to SCHED_FIFO.

	t = kthread_run(..., "rcuog/%d", ...);
	...
	if (kthread_prio)
		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);

Thanks.