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

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Date:	Mon, 11 Jun 2012 11:26:12 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Rusty Russell <rusty@...tcorp.com.au>
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 Sun, 10 Jun 2012, Rusty Russell wrote:

> 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()).

Makes sense. Will have a go on that.

One other thing what I'm thinking about is to avoid the synchronous
parking mechanism, i.e. just tell the thread to park and check the
park state later before going further down.

Thanks,

	tglx
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