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

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Date:	Thu, 12 Jul 2007 11:49:57 -0700 (PDT)
From:	david@...g.hm
To:	Mark Lord <lkml@....ca>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Huang, Ying" <ying.huang@...el.com>, Pavel Machek <pavel@....cz>,
	nigel@...el.suspend2.net, Jeremy Maitin-Shepard <jbms@....edu>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

On Thu, 12 Jul 2007, Mark Lord wrote:

> Rafael J. Wysocki wrote:
>>  On Thursday, 12 July 2007 08:43, david@...g.hm wrote:
>> >  On Wed, 11 Jul 2007, Jeremy Fitzhardinge wrote:
>> > 
>> > >  Andrew Morton wrote:
> ..
>> >  8. hibernate kernel does syspend-to-ram to put the devices into a known 
>> >  safe state.
>>  Again, the devices should be quiesced rather then suspended in this step.
>
> That's just not possible.  The Hibernate kernel will not have all
> of the same device drivers as the mainline kernel.  Or at least that's
> what people have previously stated here.

devices that have not been touches don't need to be quiesced or put into a 
low-power state, they are still waiting to be initialized. so as long as 
the device initialization can be done from the low-power or quiesced state 
things will work just fine.

> ..
>> > > >   This sounds awesome.  Am I correct in expecting that ultimately the
>> > > >   existing hibernation implementation just goes away and we reuse 
>> > > >   (and hence
>> > > >   strengthen) the existing kexec (and kdump?) infrastructure?
>
> No, not so simple.  We still need much of the code to santize devices
> upon wakeup from hibernation.   And adding this extra reboot-kernel step
> in the midst of hibernate will double the time it takes (ugh).
>
> Currently, TuxOnIce(suspend2) takes about 10 seconds to suspend my notebook.
> Switching to this new scheme would double that to 10 seconds to boot/probe,
> plus the original 10 seconds to hibernate.  Assuming the new implementation
> even comes close to suspend2 speed.

why do you assume that it will take 10 seconds to boot the new kernel? 
linuxbiosdoes it in <2 seconds, someone else posted on this thread <5 
seconds

> And the complexity and difficulty of setup really scares me.
> Right now, we've got a pretty good/fast in-kernel (well, external patch)
> that allows my machines to hibernate very quickly, wake up even faster,
> and not swap like mad afterwards.  Without any external programs,
> initramfs, or extra kernels required.
>
> And we want to replace this with an ultra-complex setup because.. ????

the complexity of the freezer freezing some things, but not other things 
keeps getting t wrong and many people can't think of any algorithm that 
will always get it right. This approach bypasses the entire problem 
makeing it much simpler conceptually, even though there are a few more 
parts involved.

David Lang
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