[ 3.5.y.z extended stable ] Patch "powerpc: fix numa distance for form0 device tree" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    powerpc: fix numa distance for form0 device tree

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 65985d82e411aca08a3ae545ad100089c2bc5d35 Mon Sep 17 00:00:00 2001
From: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>
Date: Fri, 22 Mar 2013 05:49:35 +0000
Subject: [PATCH] powerpc: fix numa distance for form0 device tree

commit 7122beeee7bc1757682049780179d7c216dd1c83 upstream.

The following commit breaks numa distance setup for old powerpc
systems that use form0 encoding in device tree.

commit 41eab6f88f24124df89e38067b3766b7bef06ddb
powerpc/numa: Use form 1 affinity to setup node distance

Device tree node /rtas/ibm,associativity-reference-points would
index into /cpus/PowerPCxxxx/ibm,associativity based on form0 or
form1 encoding detected by ibm,architecture-vec-5 property.

All modern systems use form1 and current kernel code is correct.
However, on older systems with form0 encoding, the numa distance
will get hard coded as LOCAL_DISTANCE for all nodes.  This causes
task scheduling anomaly since scheduler will skip building numa
level domain (topmost domain with all cpus) if all numa distances
are same.  (value of 'level' in sched_init_numa() will remain 0)

Prior to the above commit:
((from) == (to) ? LOCAL_DISTANCE : REMOTE_DISTANCE)

Restoring compatible behavior with this patch for old powerpc systems
with device tree where numa distance are encoded as form0.

Signed-off-by: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <michael at ellerman.id.au>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/powerpc/mm/numa.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 1e95556..4ec32a6 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -201,7 +201,7 @@ int __node_distance(int a, int b)
 	int distance = LOCAL_DISTANCE;

 	if (!form1_affinity)
-		return distance;
+		return ((a == b) ? LOCAL_DISTANCE : REMOTE_DISTANCE);

 	for (i = 0; i < distance_ref_points_depth; i++) {
 		if (distance_lookup_table[a][i] == distance_lookup_table[b][i])
--
1.8.1.2