Re: [patch 04/17] Add pagetable accessors to pack and unpack pagetable entries

Ingo Molnar
2007-04-04T15:48:10Z

* Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> Ingo Molnar wrote:
> > the main metric we are interested in is the overhead for people who just
> > want to run the non-patched native kernel that has CONFIG_PARAVIRT
> > enabled (99%+ of the users at the moment), so the delta is:
> >
> > null: +12.0%
> > null IO: +7.5%
> > stat: within noise
> > open/close: within noise
> > TCP: ~5.0%
> > signal install: 2.0%
> > signal handle: 4.7%
> > fork: 2.7%
> > exec: 3.6%
> > shell: 3.6%
> >
>
> Hm, I don't think you can get this much precision out of these
> numbers. I noticed larger variations from boot-to-boot running the
> same test.

sure. i simply took the middle numbers. But there's definitely a 'few
percents' trend in the numbers.

> > this is not 'barely measurable' but 'BLOODY LARGE' overhead.
>
> Yes. Fortunately there's a noticable difference between native and
> unpatched paravirt, because it shows all the effort we put into
> patching is worthwhile.

if only it were not such an ugly piece of code? ;)

Ingo