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SubjectRe: [patch 1/5] sched: remove degenerate domains
On Wed, Apr 06, 2005 at 07:44:12AM +0200, Ingo Molnar wrote:
>
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> > This is Suresh's patch with some modifications.
>
> > Remove degenerate scheduler domains during the sched-domain init.
>
> actually, i'd suggest to not do this patch. The point of booting with a
> CONFIG_NUMA kernel on a non-NUMA box is mostly for testing, and the

Not really. All of the x86_64 kernels are NUMA enabled and most Intel x86_64
systems today are non NUMA.

> 'degenerate' toplevel domain exposed conceptual bugs in the
> sched-domains code. In that sense removing such 'unnecessary' domains
> inhibits debuggability to a certain degree. If we had this patch earlier
> we'd not have experienced the wrong decisions taken by the scheduler,
> only on the much rarer 'really NUMA' boxes.
>
> is there any case where we'd want to simplify the domain tree? One more
> domain level is just one (and very minor) aspect of CONFIG_NUMA - i'd
> not want to run a CONFIG_NUMA kernel on a non-NUMA box, even if the
> domain tree got optimized. Hm?
>

Ingo, pardon me! Actually I used NUMA domain as an excuse to push domain
degenerate patch.... As I mentioned earlier, we should remove SMT domain
on a non-HT capable system.

Similarly I am working on adding a new core domain for dual-core systems!
All these domains are unnecessary and cause performance isssues on
non Multi-threading/Multi-core capable cpus! Agreed that performance
impact will be minor but still...

thanks,
suresh
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