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

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Date:	Thu, 21 Apr 2011 11:04:27 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andreas Herrmann <herrmann.der.user@...glemail.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	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)

> 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? 

> 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.

Download attachment "0001-Revert-x86-NUMA-Fix-fakenuma-boot-failure.patch" of type "application/octet-stream" (4840 bytes)

Download attachment "0002-x86-64-NUMA-reimplement-cpu-node-map-initialization-.patch" of type "application/octet-stream" (3777 bytes)