Hi,
On Friday, 21 of January 2005 00:06, Pavel Machek wrote:
> Hi!
>
> > > > The readability of code is also important, IMHO.
> > >
> > > It did not seem too much better to me.
> >
> > Well, the beauty is in the eye of the beholder. :-)
> >
> > Still, it shrinks the code (22 lines vs 37 lines), it uses less GPRs (5 vs
> > 7), it uses less
> > SIB arithmetics (0 vs 4 times), it uses a well known scheme for copying
> > data pages.
> > As far as the result is concerned, it is equivalent to the existing code,
> > but it's simpler
> > (and faster). IMO, simpler code is always easier to understand.
> >
> >
> > > > > If you want cheap way to speed it up, kill cr3 manipulation.
> > > >
> > > > Sure, but I think it's there for a reason.
> > >
> > > Reason is "to crash it early if we have wrong pagetables".
> > >
> > > > > Anyway, this is likely to clash with hugang's work; I'd prefer this
> > > > > not to be applied.
> > > >
> > > > I am aware of that, but you are not going to merge the hugang's patches
> > > > soon, are you?
> > > > If necessary, I can change the patch to work with his code (hugang,
> > > > what do you think?).
> > >
> > > I think it is just not worth the effort.
> >
> > Why? It won't take much time. I've spent more time for writing the
> > messages
> > in this thread ... ;-)
>
> 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.
> And it is hand-made, not C produced.
Yes, it is.
> So... your code may be better but I do not think it is so much better
> that I'd like to risk it.
Now, that's clear. :-)
Anyway, if anyone could test it or look at it and say a word, please do so.
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"
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