linux-kernel - Re: Off topic: Numactl "distance" wrong

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Message-ID: <49D66E83.5070606@inria.fr>
Date:	Fri, 03 Apr 2009 22:16:03 +0200
From:	Brice Goglin <Brice.Goglin@...ia.fr>
To:	Chris Worley <worleys@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Off topic: Numactl "distance" wrong

Chris Worley wrote:
> Sorry for an off topic, but I'm hoping somebody can point me in the
> right direction of where to direct this question...
>
> I have an Opteron system where I've seen the HW diagrams, and each of
> 4 sockets is directly connected (HT) to two other sockets, and two HT
> hops away from a third (i.e. a simple square topology, no X in the
> middle).
>
> Yet, "numactl --hardware" shows but one hop to each socket:
>
> # numactl --hardware
> ...
> node   0   1   2   3
>   0:  10  20  20  20
>   1:  20  10  20  20
>   2:  20  20  10  20
>   3:  20  20  20  10
>
> I know this is wrong.
>
> Who would be the right person (or list) to talk about this?
>   

IIRC, the motherboard/BIOS is supposed to report numa distances through
the PXM ACPI method. But I have never seen any opteron box do it
properly. So you just get 10 for "local" and 20 for "remote". Some
Itanium machines however report actual distances.

Brice

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