Re: Break 2.4 VM in five easy steps

[Bernd Jendrissek]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Mon, Jun 11, 2001 at 04:04:45PM -0300, Rik van Riel wrote:
> On Mon, 11 Jun 2001, Maciej Zenczykowski wrote:
> > On Fri, 8 Jun 2001, Pavel Machek wrote:
> >
> > > That modulo is likely slower than dereference.
> > >
> > > > +               if (count % 256 == 0) {
> >
> > You are forgetting that this case should be converted to and 255
> > or a plain byte reference by any optimizing compiler

You read too much into my choice - 256 is a random number ;)

> What matters is that this thing calls schedule() unconditionally
> every 256th time.  Checking current->need_resched will only call
> schedule if it is needed ... not only that, but it will also
> call schedule FASTER if it is needed.

I will try this later today, but it seems right enough.

generic_file_write seems to do enough other work that a dereference
vs. and-255 shouldn't be too bad...

Bernd Jendrissek
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.4 (GNU/Linux)
Comment: For info see http://www.gnupg.org

iD8DBQE7Jciz/FmLrNfLpjMRAmI9AKCm2EYziCzG0qrobFooGLf3kepb/wCbBQf6
nXmD/OZNhGttwQejZtYi3ic=
=rWL2
-----END PGP SIGNATURE-----