Re: [rfc 08/45] cpu alloc: x86 support

Nick Piggin
2007-11-20T04:00:26Z

On Tuesday 20 November 2007 13:02, Christoph Lameter wrote:
> On Mon, 19 Nov 2007, H. Peter Anvin wrote:
> > You're making the assumption here that NUMA = large number of CPUs. This
> > assumption is flat-out wrong.
>
> Well maybe. Usually one gets to NUMA because the hardware gets too big to
> be handleed the UMA way.
>
> > On x86-64, most two-socket systems are still NUMA, and I would expect
> > that most distro kernels probably compile in NUMA. However,
> > burning megabytes of memory on a two-socket dual-core system when we're
> > talking about tens of kilobytes used would be more than a wee bit insane.
>
> Yeah yea but the latencies are minimal making the NUMA logic too expensive
> for most loads ... If you put a NUMA kernel onto those then performance
> drops (I think someone measures 15-30%?)

Small socket count systems are going to increasingly be NUMA in future.
If CONFIG_NUMA hurts performance by that much on those systems, then the
kernel is broken IMO.