linux-kernel - Re: Linux 2.6.39-rc4 (regression: NUMA on multi-node CPUs broken)

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Date:	Thu, 21 Apr 2011 08:04:17 +0200
From:	Andreas Herrmann <herrmann.der.user@...glemail.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>
Subject: Re: 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@...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@....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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