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

From: Linus Torvalds
Date: Wed Apr 25 2007 - 18:19:34 EST

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".


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.

I'll tell you: Nada. Zero. Zilch. Nothing.

"Freeze" for a disk is a total no-op. There is no DMA, there is no
nothing. In contrast, "suspend" for a disk is a totally valid operation.

Anybody who claims that these two operations are "related" is a moron.

I'm sorry Pavel, but that's exactly how it is.

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