linux-kernel - Re: suspend2 merge (was Re: [Suspend2-devel] Re: CFS and suspend2: hang in atomic copy)

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Date:	Thu, 26 Apr 2007 08:27:07 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Pavel Machek <pavel@....cz>, Kenneth Crudup <kenny@...ix.com>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Con Kolivas <kernel@...ivas.org>,
	suspend2-devel@...ts.suspend2.net, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: suspend2 merge (was Re: [Suspend2-devel] Re: CFS and suspend2:
	hang in atomic copy)

Hi.

On Wed, 2007-04-25 at 15:18 -0700, Linus Torvalds wrote:
> 
> On Wed, 25 Apr 2007, Pavel Machek wrote:
> > 
> > Not the same... but they are still related. "freeze" (for atomic
> > snapshot) is actually subset of "suspend"... freeze needs DMAs off and
> > saved state, and you need DMAs off and saved state for "suspend".
> 
> THEY HAVE ABSOLUTELY NOTHING IN COMMON!
> 
> Nobody in their right mind thinks that "disable DMA" and "suspend" are 
> similar operations. 
> 
> > So it is actually correct to do "suspend" when you want "freeze"; it
> > is just slow. That's why they only differ in parameter these days.
> 
> It is *not* correct to "suspend" when you want "freeze".
> 
> I don't understand how you can even *claim* something like that.
> 
> Here's a trivial example:
>  - SCSI disk
> 
> Tell me, what does "suspend" do, and what does "freeze" (snapshot) do?
> 
> And name *one* thing that have in common.

Set/reset the scsi transaction id thingy? Hibernation didn't work with
SCSI for a long time precisely because that support was missing.

Don't get me wrong, I agree on the whole - Suspend2 worked fine on the
whole under 2.4 without a driver model. But they do have a bit in
common.

Regards,

Nigel

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