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SubjectRe: NUMA emulation x86_64: numa=fake parameter for custom nodes distance
On Sat, 19 Nov 2011, Petr Holasek wrote:

> A lot of developers still have no access to large NUMA machines and
> possibility of NUMA emulation could involve more of them to thinking
> about NUMA awareness of their apps/kernel code.
>

That's a bogus argument, numa=fake already allows you to construct as
large of a NUMA box as you want in a faked environment. The distances
have nothing to do with that.

The distances you're adding here are, by definition, incorrect because it
doesn't respect the actual distance between physical nodes that numa=fake
uses already. If you're using numa=fake on an UMA machine, then the
performance of the kernel will be just that, you won't actual see any
introduced latency between fake nodes just by changing the distance. So
you're completely invalidating what internode distances actually mean.

I'd much rather see an option to fake the SLIT that could do all of this
without limitation and would be possible to debug issues in the future.


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