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SubjectRe: 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@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). 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.

With this patch Linux shows

root # numactl --hardware
available: 8 nodes (0-7)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11
node 0 size: 8189 MB
node 0 free: 7937 MB
node 1 cpus:
node 1 size: 16384 MB
node 1 free: 16129 MB
node 2 cpus: 12 13 14 15 16 17 18 19 20 21 22 23
node 2 size: 8192 MB
node 2 free: 8024 MB
node 3 cpus:
node 3 size: 16384 MB
node 3 free: 16129 MB
node 4 cpus: 24 25 26 27 28 29 30 31 32 33 34 35
node 4 size: 8192 MB
node 4 free: 8013 MB
node 5 cpus:
node 5 size: 16384 MB
node 5 free: 16129 MB
node 6 cpus: 36 37 38 39 40 41 42 43 44 45 46 47
node 6 size: 8192 MB
node 6 free: 8025 MB
node 7 cpus:
node 7 size: 16384 MB
node 7 free: 16128 MB
node distances:
node 0 1 2 3 4 5 6 7
0: 10 16 16 22 16 22 16 22
1: 16 10 22 16 16 22 22 16
2: 16 22 10 16 16 16 16 16
3: 22 16 16 10 16 16 22 22
4: 16 16 16 16 10 16 16 22
5: 22 22 16 16 16 10 22 16
6: 16 22 16 22 16 22 10 16
7: 22 16 16 22 22 16 16 10


which is bogus. The correct NUMA-information (based on SRAT) (w/o this
patch) is

linux # numactl --hardware
available: 8 nodes (0-7)
node 0 cpus: 0 1 2 3 4 5
node 0 size: 8189 MB
node 0 free: 7947 MB
node 1 cpus: 6 7 8 9 10 11
node 1 size: 16384 MB
node 1 free: 16114 MB
node 2 cpus: 12 13 14 15 16 17
node 2 size: 8192 MB
node 2 free: 7941 MB
node 3 cpus: 18 19 20 21 22 23
node 3 size: 16384 MB
node 3 free: 16120 MB
node 4 cpus: 24 25 26 27 28 29
node 4 size: 8192 MB
node 4 free: 8028 MB
node 5 cpus: 30 31 32 33 34 35
node 5 size: 16384 MB
node 5 free: 16116 MB
node 6 cpus: 36 37 38 39 40 41
node 6 size: 8192 MB
node 6 free: 8033 MB
node 7 cpus: 42 43 44 45 46 47
node 7 size: 16384 MB
node 7 free: 16120 MB
node distances:
node 0 1 2 3 4 5 6 7
0: 10 16 16 22 16 22 16 22
1: 16 10 22 16 16 22 22 16
2: 16 22 10 16 16 16 16 16
3: 22 16 16 10 16 16 22 22
4: 16 16 16 16 10 16 16 22
5: 22 22 16 16 16 10 22 16
6: 16 22 16 22 16 22 10 16
7: 22 16 16 22 22 16 16 10



Regards,

Andreas


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