Re: [patch] sched: auto-tune migration costs [was: Re: Industry db benchmark result on recent 2.6 kernels]

[Nick Piggin <nickpiggin@yahoo.com.au>]

Paul Jackson wrote:
> Ingo wrote:
>
> > if you create a sched-domains hierarchy (based on the SLIT tables, or in 
> > whatever other way) that matches the CPU hierarchy then you'll 
> > automatically get the proper distances detected.
>
>
> Yes - agreed.  I should push in the direction of improving the
> SN2 sched domain hierarchy.

I'd just be a bit careful about this. Your biggest systems will have
what? At least 7 or 8 domains if you're just going by the number of
hops, right? And maybe more if there is more to your topology than
just number of hops.

sched-domains firstly has a few problems even with your 2 level NUMA
domains (although I'm looking at fixing them if possible), but also
everything just has to do more work as you traverse the domains and
scan all CPUs for balancing opportunities. And its not like the cpu
scheduler uses any sort of exact science to make choices...

Nick

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