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Subject[PATCH] Fix fake numa on ppc
Hello,

Below is a patch to fix a couple of issues with fake numa node creation
on ppc:

1) Presently, fake nodes could be created such that real numa node
boundaries are not respected. So a node could have lmbs that belong to
different real nodes.
2) The cpu association is broken. On a JS22 blade for example, which is
a 2-node numa machine, I get the following:

# cat /proc/cmdline
root=/dev/sda6 numa=fake=2G,4G,,6G,8G,10G,12G,14G,16G
# cat /sys/devices/system/node/node0/cpulist
0-3
# cat /sys/devices/system/node/node1/cpulist
4-7
# cat /sys/devices/system/node/node4/cpulist

#

So, though the cpus 4-7 should have been associated with node4, they
still belong to node1. The patch works by recording a real numa node
boundary and incrementing the fake node count. At the same time, a
mapping is stored from the real numa node to the first fake node that
gets created on it.

Any suggestions on improving the patch are most welcome!

Signed-off-by: Ankita Garg <ankita@in.ibm.com>

Index: linux-2.6.31-rc5/arch/powerpc/mm/numa.c
===================================================================
--- linux-2.6.31-rc5.orig/arch/powerpc/mm/numa.c
+++ linux-2.6.31-rc5/arch/powerpc/mm/numa.c
@@ -26,6 +26,11 @@
#include <asm/smp.h>

static int numa_enabled = 1;
+static int fake_enabled = 1;
+
+/* The array maps a real numa node to the first fake node that gets
+created on it */
+int fake_numa_node_mapping[MAX_NUMNODES];

static char *cmdline __initdata;

@@ -49,14 +54,24 @@ static int __cpuinit fake_numa_create_ne
unsigned long long mem;
char *p = cmdline;
static unsigned int fake_nid;
+ static unsigned int orig_nid = 0;
static unsigned long long curr_boundary;

/*
* Modify node id, iff we started creating NUMA nodes
* We want to continue from where we left of the last time
*/
- if (fake_nid)
+ if (fake_nid) {
+ if (orig_nid != *nid) {
+ fake_nid++;
+ fake_numa_node_mapping[*nid] = fake_nid;
+ orig_nid = *nid;
+ *nid = fake_nid;
+ return 0;
+ }
*nid = fake_nid;
+ }
+
/*
* In case there are no more arguments to parse, the
* node_id should be the same as the last fake node id
@@ -440,7 +455,7 @@ static int of_drconf_to_nid_single(struc
*/
static int __cpuinit numa_setup_cpu(unsigned long lcpu)
{
- int nid = 0;
+ int nid = 0, new_nid;
struct device_node *cpu = of_get_cpu_node(lcpu, NULL);

if (!cpu) {
@@ -450,8 +465,15 @@ static int __cpuinit numa_setup_cpu(unsi

nid = of_node_to_nid_single(cpu);

+ if (fake_enabled && nid) {
+ new_nid = fake_numa_node_mapping[nid];
+ if (new_nid > 0)
+ nid = new_nid;
+ }
+
if (nid < 0 || !node_online(nid))
nid = any_online_node(NODE_MASK_ALL);
+
out:
map_cpu_to_node(lcpu, nid);

@@ -1005,8 +1027,11 @@ static int __init early_numa(char *p)
numa_debug = 1;

p = strstr(p, "fake=");
- if (p)
+ if (p) {
cmdline = p + strlen("fake=");
+ if (numa_enabled)
+ fake_enabled = 1;
+ }

return 0;
}
--
Regards,
Ankita Garg (ankita@in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India


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