linux-kernel - Re: [PATCH] kthread: Implement park/unpark facility

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Message-ID: <878vfviv1h.fsf@rustcorp.com.au>
Date:	Sun, 10 Jun 2012 15:10:42 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...e.hu>,
	H Peter Anvin <hpa@...or.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Tony Luck <tony.luck@...el.com>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Arjan Dan De Ven <arjan@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>, linux-pm <linux-pm@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH] kthread: Implement park/unpark facility

On Tue, 5 Jun 2012 15:41:48 +0200 (CEST), Thomas Gleixner <tglx@...utronix.de> wrote:
> Subject: kthread: Implement park/unpark facility
> From: Thomas Gleixner <tglx@...utronix.de>
> Date: Wed, 18 Apr 2012 16:37:40 +0200
> 
> To avoid the full teardown/setup of per cpu kthreads in the case of
> cpu hot(un)plug, provide a facility which allows to put the kthread
> into a park position and unpark it when the cpu comes online again.

Like the idea, but the API is awkward.  Now you've made returning from a
thread do different things depending on whether it was parked or not.

How about just have the thread call "kthread_parkme()" which only
returns if/when the thread is unparked?

So the thread does:

        while (!kthread_should_stop()) {
                if (kthread_should_park()) {
                        ... cleanup ...
                        kthread_parkme();
                        ... restore ...
                }
                ... work ...
        }

Threads which never exit have "for (;;)" instead of while
(!kthread_should_stop()).

Cheers,
Rusty.
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