Re: [Patch] sched: remove unnecessary sched domains

[Nick Piggin]

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.

Thanks

--
SUSE Labs, Novell Inc.

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