Re: [rfc 08/45] cpu alloc: x86 support
From: H. Peter Anvin
Date: Mon Nov 19 2007 - 21:19:37 EST
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%?)
How do you handle this memory, in the first place? Do you allocate the
whole 2 MB for the particular CPU, or do you reclaim the upper part of
the large page? (I haven't dug far enough into the source to tell.)
-hpa
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