Re: [Patch] sched: remove unnecessary sched domains

["Siddha, Suresh B" <suresh.b.siddha@intel.com>]

On Sat, Apr 02, 2005 at 12:07:27PM +1000, Nick Piggin wrote:
> Siddha, Suresh B wrote:
> > Appended patch removes the unnecessary scheduler domains(containing
> > only one sched group) setup during the sched-domain init.
> > 
> > For example on x86_64, we always have NUMA configured in. On Intel EM64T
> > systems, top most sched domain will be of NUMA and with only one sched_group in
> > it. 
> > 
> > With fork/exec balances(recent Nick's fixes in -mm tree), we always endup 
> > taking wrong decisions because of this topmost domain (as it contains only 
> > one group and find_idlest_group always returns NULL). We will endup loading 
> > HT package completely first, letting active load balance kickin and correct it.
> > 
> > In general, this patch also makes sense with out recent Nick's fixes
> > in -mm.
> > 
> 
> Yeah, this makes sense. We may want to add some other criteria on the
> removal of a domain as well (because some of the domain flags do things
> that don't use groups).
> 
> I don't like so much that we'd rely on it to fix the above problem.
> There are a general class of problems with the fork/exec balancing in
> that it only works on the top most domain, so it may not spread load over
> lower domains very well.
> 
> I was thinking we could fix that by running balance on fork/exec multiple
> times from top to bottom level domains. I'll have to measure the cost of
> doing that, because it may be worthwhile.

Agreed.

BTW, why are we setting SD_BALANCE_FORK flag for NUMA domain on i386, ia64.
This should be set only on x86_64 and that too not for Intel systems.

thanks,
suresh