Re: NUMA and SMP

[Ryan Harper <ryanh@us.ibm.com>]

* David Pilger <pilger.david@gmail.com> [2007-01-14 06:04]:
> Hi all,
> 
> 1. Does desktop computers, such as intel dual core really benefit from NUMA?

Desktop computers with AMD chips which include a memory bus on the cpu
have NUMA characteristics that can benefit from keeping memory close to
the cpu.

> 2. Does it have a real effect on the performance of Xen?

I've [1]posted previously to the list on the performance benefit for NUMA
systems and that there is no regression for non-NUMA systems.

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

Xen owns all of the system memory and also controls the allocation of
that memory and therefor determines what memory and which processors are
in use for a guest.  If we are to be able to create a guest with memory
close to the physical processors in-use, then we must understand the
topology of the system when we allocate memory for the guest.

I'm not sure I understand entirely what you mean by letting the guest OS
manage NUMA instead.  However, the current Xen NUMA implementation does
not export the domain's NUMA-ness to the guest kernel, but that is the
next logical step.  Not only allocate memory to the guest in a
NUMA-aware fashion, but in the case that we are required to give memory
to a guest from multiple NUMA nodes, to export the guest topology such
that if the guest OS is NUMA-aware, it can make NUMA-aware decisions.


1. http://lists.xensource.com/archives/html/xen-devel/2006-09/msg00958.html

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com