linux-kernel - Re: [RFD] CPU hotplug and suspend

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Message-ID: <20070409140352.GB3864@ucw.cz>
Date:	Mon, 9 Apr 2007 14:03:52 +0000
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [RFD] CPU hotplug and suspend

Hi!

> Currently, we use the CPU hotplug to disable nonboot CPUs in the suspend code
> paths, but with the recent change of code ordering (ie. nonboot CPUs are
> disabled after freezing tasks _and_ devices) it has become quite troublesome.
> The reason of this is that there are some CPU hotplug notifiers registered and
> called on each run of cpu_up()/cpu_down() that assume the system to be fully
> functional, which is not the case during the suspend.  Moreover, at least some
> of them do things that are not really necessary for disabling or enabling the
> nonboot CPUs.

Right.

> The advantage of using the CPU hotplug (in its current form) for suspending is
> that if some CPUs don't reappear during the resume, we are safe.  Still, I
> think it would be more appropriate, and simpler in the long run, to notify the
> interested subsystems _only_ if one (or more) CPUs are not functional after the
> resume. 

I'm afraid that adding 'cpu not there so simulate unplug' path will
make it complex, and prone to failure, as _noone_ is going to test it.

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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