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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Pavel Machek <pavel@suse.cz>
Subject: Re: [PATCH][RFC] swsusp: speed up image restoring on x86-64
Date: Fri, 21 Jan 2005 13:43:40 +0100
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On Friday, 21 of January 2005 11:06, Pavel Machek wrote:
> Hi!
> 
> > > Well, I know that current code works. It was produced by C compiler,
> > > btw. Now, new code works for you, but it was not in kernel for 4
> > > releases, and... this code is pretty subtle.
> > 
> > Now, I'm confused. :-)  It's roughly this:
> > 
> > struct pbe *pbe = pagedir_nosave, *end;
> > unsigned n = nr_copy_pages;
> > if (n) {
> > 	end = pbe + n;
> > 	do {
> > 		memcpy((void *)pbe->orig_address, (void *)pbe->address, PAGE_SIZE);
> > 		pbe++;
> > 	} while (pbe < end);
> > }
> > 
> > where memcpy() is of course a hand-written inline that includes the cr3 manipulation,
> > and pbe, end, n are registers.
> 
> For example it may not use any variable in memory, and may not use
> stack, as memory changes under its hands.

Which is not a big problem on x86-64. :-)

> Plus assembly is always subtle ;-).

And that's what makes it interesting.

Greets,
RJW


-- 
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
		-- Lewis Carroll "Alice's Adventures in Wonderland"