Re: Allow to change SD_NODES_PER_DOMAIN at configuration or boot

[Xavier Bru <xavier.bru@bull.net>]

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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 ?
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.
Providing SD_NODES_PER_DOMAIN as a boot parameter was also intended to 
choose between a multilevel sched-domains or not.

-- 

	Sincères salutations.


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