Re: [2.6 patch] i386: always use 4k stacks

Ingo Molnar
2005-11-16T09:19:09Z

* Oliver Neukum <oliver@neukum.org> wrote:

> Am Mittwoch, 16. November 2005 09:03 schrieb Arjan van de Ven:
> > * less CPU cache footprint due to interrupt stacks
> >    - interrupt stacks are per cpu now instead of borrowing the per
> >      thread stack space; this both has less impact on the caches, and
> >      has more cache hits; the per cpu stack will be in cache more than
> >      the previously scattered bits and pieces
> > * more stack space is available for interrupts compared to 2.4 kernels
> >    - in 2.4 kernels only 2Kb was available for interrupt context (to
> >      keep 4K available for user context). With complex softirqs such as
> >      PPP and firewall rules and nested interrupts this wasn't always
> >      enough. Compared to 2.6-with-8Kstacks is a bit harder; there is
> >      2Kb extra available there compared to 2.4 and arguably some of that
> >      extra is for interrupts.
>
> This is due to having interrupt stacks. Is there any reason not to
> have 8K task stacks and per CPU interrupt stacks?

yes, all the other arguments you snipped :) Arjan wrote 4K+4K stacks for
Fedora almost 2 years ago, and the patch has a good track record. Here's
some more background info about 4K+4K stacks:

http://lwn.net/Articles/84583/
http://lwn.net/Articles/150580/
http://lwn.net/Articles/160138/

Ingo