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SubjectRe: Linux 2.6.39-rc4 (regression: NUMA on multi-node CPUs broken)
On Thu, Apr 21, 2011 at 11:04:27AM +0900, KOSAKI Motohiro wrote:
> > 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?

It's

commit 5a925b4282d7f805deafde62001a83dbaf8be275
Author: Andreas Herrmann <andreas.herrmann3@amd.com>
Date: Thu Sep 3 09:44:28 2009 +0200

x86, sched: Workaround broken sched domain creation for AMD Magny-Cours



> > 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.


Andreas


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