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    SubjectRe: NUMA or not on dual Opteron
    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.

    Justin
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