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SubjectRe: Linux 2.6.39-rc4 (regression: NUMA on multi-node CPUs broken)
Date
> Following patch breaks real NUMA on multi-node CPUs like AMD
> Magny-Cours and should be reverted (or changed to just take effect in
> case of numa=fake):
>
> commit 7d6b46707f2491a94f4bd3b4329d2d7f809e9368
> Author: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Date: Fri Apr 15 20:39:01 2011 +0900
>
> x86, NUMA: Fix fakenuma boot failure
>
> ...
>
> Thus, this patch implements a reassignment of node-ids if buggy firmware
> or numa emulation makes wrong cpu node map. Tt enforce all logical cpus
> in the same physical cpu share the same node.
>
> ...
>
> +static void __cpuinit check_cpu_siblings_on_same_node(int cpu1, int cpu2)
> +{
> + int node1 = early_cpu_to_node(cpu1);
> + int node2 = early_cpu_to_node(cpu2);
> +
> + /*
> + * Our CPU scheduler assumes all logical cpus in the same physical cpu
> + * share the same node. But, buggy ACPI or NUMA emulation might assign
> + * them to different node. Fix it.
> + */
>
> ...
>
> This is a false assumption. Magny-Cours has two nodes in the same
> physical package. The scheduler was (kind of) fixed to work around
> this boot problem for multi-node CPUs (with 2.6.32).

I agree we have to fix this ASAP. I also think we have to avoid reintroduce
the same again. Can you please tell me the commit-id of this one?

> If this is also
> an issue with wrong cpu node maps in case of NUMA emulation this might
> be fixed similar or this quirk should only be applied in case of NUMA
> emulation.

Indeed.

Tejun, Do you remember I sent numa emulation specific patch at first. now
I'm beside with Andreas. Because I bet current numa fallback code (you
pointed out one) has no user.

Or, please let us know if you have an alternative patch.



Attached revert and fakenuma spefic fix patches.
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