linux-kernel - Re: [linux-pm] Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

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Message-Id: <200707131731.36113.rjw@sisk.pl>
Date:	Fri, 13 Jul 2007 17:31:35 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	david@...g.hm, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@....cz>,
	"Huang, Ying" <ying.huang@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org,
	Jeremy Maitin-Shepard <jbms@....edu>
Subject: Re: [linux-pm] Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

On Friday, 13 July 2007 16:37, Alan Stern wrote:
> On Fri, 13 Jul 2007, Rafael J. Wysocki wrote:
> 
> > > I missed this discussion. is this idea to suspend, write to disk, but 
> > > leave things in ram so that if you wakeup soon enough you have everything 
> > > for ram, but if you don't and the battery dies you can restore from disk?
> > > 
> > > if so I think it's a mistake to mix the two. it would be better to just 
> > > suspend to ram, and wake up once in a while to check the battery state and 
> > > when the battery gets low enough do the suspend to disk.
> > > 
> > > otherwise you end up mixing the requirements of the two types of suspend, 
> > > which is how things got so ugly in the first place.
> > 
> > Not necessarily.  If we don't put devices into low power states before creating
> > the image, that should work just fine (quiesce devices, create the image or
> > kexec the new kernel, reprobe devices, save the image, suspend to RAM,
> > resume from RAM, continue - or restore from the image if power failed in the
> > meantime).  Still, for this purpose, both kernels need to be able to handle the
> > same set of devices.
> 
> Why?
> 
> Suppose the kexec kernel can't handle some device.  The normal kernel 
> has already quiesced the device, so it will remain quiescent while the 
> kexec kernel runs and throughout the suspend.  When the regular kernel 
> regains control the device will be ready for use.  I don't see any 
> problem.

On an ACPI system the device may be in a power state that doesn't allow us to
enter S3 (in theory, that is).

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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