Messages in this thread |  | | | Date | Thu, 13 Jan 2005 11:07:33 -0600 | | From | "Justin M. Forbes" <> | | Subject | Re: NUMA or not on dual Opteron |
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On Thu, Jan 13, 2005 at 11:02:19AM +0100, Raphael Jacquot wrote: > >I was under the impression that NUMA is useful on > 2-way systems only. > >Is this true, and if not, under what circumstances is NUMA useful on > >2-way Opteron systems? > > > >In other words: why should one want NUMA to be enabled or disabled for > >dual Opteron? > > > >Thanks in advance. > > > > Numa needs to be enabled on bi-opteron systems because each processor > controls part of the memory. unlike the intel memory architecture, where > processors share the same bus to access memory. > Numa in opteron systems is thus required to allow sharing of memory .
This is somewhat true. There are 2 types of dual opteron boards. Those in the $200 US range only have one memory bank, which is attached to CPU0. They operate as a single node, and may perform better with numa turned off. Those in the $400+ range tend to have one bank per CPU and will certainly perform better with numa on. They do usually have a bios option to interleave the nodes which would show up as a single node, and probably perform better with numa turned off, but a better solution is to turn off the node interleave in bios and run the kernel with numa support. Basically if you have 2 CPUs and only one memory bank, maybe turning numa off will give better performance, but if you have one memory bank per CPU numa should be on.
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