Re: Break 2.4 VM in five easy steps

Bernd Jendrissek
2001-06-12T07:50:43Z

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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
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