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

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Message-ID: <Pine.LNX.4.64.0711191759370.19954@schroedinger.engr.sgi.com>
Date:	Mon, 19 Nov 2007 18:02:11 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	ak@...e.de, akpm@...ux-foundation.org, travis@....com,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc 08/45] cpu alloc: x86 support

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%?)

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