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Enable NUMA behaviour on a Core i7
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Well.Heeled.Man
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PostPosted: Mon Oct 31, 2011 11:31 am    Post subject: Enable NUMA behaviour on a Core i7 Reply with quote

I just have a quick question about NUMA on my Core i7 2630QM.

I am playing around with my kernel config, just to experiment. I enabled the option 'Processor type and features' -> 'enable maximum number or SMP cores and NUMA nodes'. The information for this states that it is architecture specific, so I assume this is optimal for my CPU (vs. 'maximum number of CPUs'). Now, if I am enabling NUMA behavior in my kernel, is an output from 'numactl --show' and 'numactl --hardware' of:

Code:
policy: default
preferred node: current
physcpubind: 0 1 2 3 4 5 6 7
cpubind: 0
nodebind: 0
membind: 0


and

Code:
available: 1 nodes (0)
node 0 cpus: 0 1 2 3 4 5 6 7
node 0 size: 8043 MB
node 0 free: 6853 MB
node distances:
node   0
  0:  10


correct? It looks like it is recognizing the CPU as only one node (and not each core), so infact is not using NUMA at all.

What are the performance implications on my clearly very small (4 core w/ hyperthreading) NUMA system? I have looked and I cannot really get definitive pros and cons on small systems. Also, would enabling 'General setup' -> 'Disable hierarchical RCU load balancing' help any?

I appreciate that I may be running before I can walk, but personally learn better quicker just by jumping in and having a play. I have done plenty of searching around, but I reckon I am at the stage where I should just ask someone who knows....
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Mepho
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PostPosted: Mon Oct 31, 2011 1:32 pm    Post subject: Reply with quote

Unless you want to mess with it, 'enable maximum number or SMP cores and NUMA nodes' should be ok on i7.

http://kernel-seeds.org/settings-03.html
Quote:
If you have a system that supports NUMA (such as a Core i7, or certain AMD chips), turn this setting on. This setting defaults to off.


It's not that you can really heavily boost performance with it, check on wiki what NUMA really is.

I think that SMP can go up to 8 cores (threads), so not much will happen w/o it. Do some testing using colivas benchmark or thread heavy compilation and see for yourself.
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sebB
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PostPosted: Mon Oct 31, 2011 6:03 pm    Post subject: Reply with quote

How to know if my computer support NUMA because I've a core i7 too?
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Mepho
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PostPosted: Mon Oct 31, 2011 6:35 pm    Post subject: Reply with quote

Afaik all i7 processors have it, however you wont probably ever use it on single processor machine.
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