Re: [Xen-devel] Re: NUMA and SMP

["ron minnich" <rminnich@xxxxxxxxx>]

On 1/15/07, Anthony Liguori <aliguori@xxxxxxxxxxxxxxxxxx> wrote:

> No.  NUMA standards Non-Uniform Memory Architecture.  It's basically a
> system where you have nodes (which are essentially independent
> computers) that are connected via a high speed bus.  Each node has it's
> own memory but through the magic of NUMA, every node can access the
> other nodes memory as if it's own.  Most NUMA systems (if not all) are
> very high end servers.
no, at this point, most NUMA servers are probably Alienware desktops
for gamers :-) Especially now that Dell is selling them. Opteron
brought NUMA into the mainstream in a big way. And desktop unit sales
trump all supercomputer sales :-) Us poor supercomputer types are,
once again, in the noise where dollar volume is concerned.

And, Linux has known for some time how to exploit the NUMA-ness of
these Opteron systems. There is even an ACPI table entry, SRAT, to
describe the NUMA-ness of a machine.


> > 2. Does it have a real effect on the performance of Xen?
>
> On a NUMA system, absolutely.  If you have a domain running on a
> particular node, you want to make sure that it's using memory that's in
> it's node if at all possible.  Accessing memory on a local node is
> considerably faster than access memory on other nodes.
Right, but it's not even close to a  factor of two on a desktop
machine like dual opteron. It's still worth being NUMA aware, however.

thanks

ron

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