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

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Message-ID: <20070416070132.GB1783@elf.ucw.cz>
Date:	Mon, 16 Apr 2007 09:01:32 +0200
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.
> 
> Does it mean you think we should stick with the current approach and sort out
> all issues as they show up, or should we go for not using the CPU hotplug for
> suspending without implementing the 'cpu not there so simulate unplug' path
> at all (eg. we can fail the resume instead)?

I'd fix the current approach, but...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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