Re: NUMA and SMP

[Anthony Liguori <aliguori@linux.vnet.ibm.com>]

David Pilger wrote:
> Hi all,
> 
> 1. Does desktop computers, such as intel dual core really benefit from 
> NUMA?

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.

> 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.  Prior to Ryan's 
NUMA work, Xen would just blindly allocate memory to a domain without 
taking into account memory locality.

> 3. Can't we let the guest OS manage NUMA instead of Xen? what is the
> difference? and why is it implemented in Xen?

If a guest OS spans multiple nodes, then you would want it to be NUMA 
aware.  However, you always want Xen to, at least, be NUMA aware so that 
it allocates memory appropriately.

Regards,

Anthony Liguori

> Thanks,
> David.