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List: linux-ia64
Subject: Re: Allow to change SD_NODES_PER_DOMAIN at configuration or boot
From: Nick Piggin <nickpiggin () yahoo ! com ! au>
Date: 2005-02-17 16:33:48
Message-ID: 4214C76C.2020804 () yahoo ! com ! au
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Xavier Bru wrote:
> Nick Piggin wrote:
>
>> Right. It may make more sense to have the setup based on some
>> maximum distance between nodes. Eg. all nodes less than distance
>> 10 away from node0 are to be in node0's first level NUMA domain
>> (the next level is always global, IIRC).
>>
>> Then you would still need some configuration option, but it would
>> appear to be a more useful metric to use.
>>
>>
>>
> Hello Nick & all,
> Do you mean that there should ever be only one NUMA sched-domain level ?
Hi,
No, I just mean that if the metric used to determine the nodes
in the lower level NUMA sched-domain is "node distance of no
greater than N", rather than "closest N nodes", you might have
a system that is easier to manage, and be less likely to have
the weird "artifacts" discussed.
> On a 2x4x4 cpus machine, we could in theory have SD_NODES_PER_DOMAIN=4,
> thus providing a 2 level NUMA sched-domain (domain 0 spans 4 cpus,
> domain 1 spans 16, domain 2 is global and spans 32).
> But it is true that this configuration does not show evident performance
> gains upon SD_NODES_PER_DOMAIN=8 (domain 0 spans 4 cpus, domain 1 is
> global and spans 32), at least on parallel compilation of the kernel.
I'd say yeah, such a system may be too small for that to make much
difference. That said, a kernel compile probably isn't too sensitive
to scheduling placement, provided it is not completely broken.
> Providing SD_NODES_PER_DOMAIN as a boot parameter was also intended to
> choose between a multilevel sched-domains or not.
>
Oh yes, that's better than nothing at all, definitely.
Nick
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