[PATCH v2] Fix fake numa on ppc

Hi,

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.

Tested the patch with the following commandlines:
numa=fake=2G,4G,6G,8G,10G,12G,14G,16G
numa=fake=3G,6G,10G,16G
numa=fake=4G
numa=fake=

For testing if the fake nodes respect the real node boundaries, I added
some debug printks in the node creation path. Without the patch, for the
commandline numa=fake=2G,4G,6G,8G,10G,12G,14G,16G, this is what I got:

fake id: 1 nid: 0
fake id: 1 nid: 0
...
fake id: 2 nid: 0
fake id: 2 nid: 0
...
fake id: 2 nid: 0
created new fake_node with id 3
fake id: 3 nid: 0
fake id: 3 nid: 0
...
fake id: 3 nid: 0
fake id: 3 nid: 0
fake id: 3 nid: 1
fake id: 3 nid: 1
...
created new fake_node with id 4
fake id: 4 nid: 1
fake id: 4 nid: 1
...

and so on. So, fake node 3 encompasses real node 0 & 1. Also,

# cat /sys/devices/system/node/node3/meminfo
Node 0 MemTotal:        2097152 kB
...
# # cat /sys/devices/system/node/node4/meminfo
Node 0 MemTotal:        2097152 kB
...


With the patch, I get:

fake id: 1 nid: 0
fake id: 1 nid: 0
...
fake id: 2 nid: 0
fake id: 2 nid: 0
...
fake id: 2 nid: 0
created new fake_node with id 3
fake id: 3 nid: 0
fake id: 3 nid: 0
...
fake id: 3 nid: 0
fake id: 3 nid: 0
created new fake_node with id 4
fake id: 4 nid: 1
fake id: 4 nid: 1
...

and so on. With the patch, the fake node sizes are slightly different
from that specified by the user.

# cat /sys/devices/system/node/node3/meminfo
Node 3 MemTotal:        1638400 kB
...
# cat /sys/devices/system/node/node4/meminfo
Node 4 MemTotal:         458752 kB
...

CPU association was tested as mentioned in the previous mail:

Without the patch,

# 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

#

With the patch,

# 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

# cat /sys/devices/system/node/node4/cpulist
4-7

Signed-off-by: Ankita Garg <redacted> 
Reviewed-by: Balbir Singh <redacted>

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 +26,13 @@
 #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 +56,29 @@ static int __cpuinit fake_numa_create_ne
 	unsigned long long mem;
 	char *p = cmdline;
 	static unsigned int fake_nid;
+	static unsigned int prev_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) {
+		/*
+		 * Moved over to the next real numa node, increment fake
+		 * node number and store the mapping of the real node to
+		 * the fake node
+		 */
+		if (prev_nid != *nid) {
+			fake_nid++;
+			fake_numa_node_mapping[*nid] = fake_nid;
+			prev_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 +462,7 @@ 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 +472,15 @@ 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 +1034,12 @@ 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   

On Wed, 2 Sep 2009, Ankita Garg wrote:

Hi,

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.

On x86_64, we can use numa=off to completely disable NUMA so that all 
memory and all cpus are mapped to a single node 0.  That's an extreme 
example of the above and is totally permissible.

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

#

This doesn't show what the true NUMA topology of the machine is, could you 
please post the output of

	$ cat /sys/devices/system/node/node*/cpulist
	$ cat /sys/devices/system/node/node*/distance
	$ ls -d /sys/devices/system/node/node*/cpu[0-8]

from a normal boot without any numa=fake?

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.

If there are multiple fake nodes on a real physical node, all cpus in that 
node should appear in the cpulist for each fake node for which it has 
local distance.

Hi David,

On Tue, Sep 01, 2009 at 11:37:05PM -0700, David Rientjes wrote:

On Wed, 2 Sep 2009, Ankita Garg wrote:

quoted

Hi,

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.

On x86_64, we can use numa=off to completely disable NUMA so that all 
memory and all cpus are mapped to a single node 0.  That's an extreme 
example of the above and is totally permissible.

quoted

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

#

This doesn't show what the true NUMA topology of the machine is, could you 
please post the output of

	$ cat /sys/devices/system/node/node*/cpulist
	$ cat /sys/devices/system/node/node*/distance
	$ ls -d /sys/devices/system/node/node*/cpu[0-8]

from a normal boot without any numa=fake?

Heres the output as requested by you:

# ls /sys/devices/system/node/
has_cpu  has_normal_memory  node0  node1  online  possible
# cat /sys/devices/system/node/node*/cpulist
0-3
4-7
# cat /sys/devices/system/node/node*/distance
10 20
20 10
# ls -d /sys/devices/system/node/node*/cpu[0-8]
/sys/devices/system/node/node0/cpu0  /sys/devices/system/node/node0/cpu3
/sys/devices/system/node/node1/cpu6
/sys/devices/system/node/node0/cpu1  /sys/devices/system/node/node1/cpu4
/sys/devices/system/node/node1/cpu7
/sys/devices/system/node/node0/cpu2  /sys/devices/system/node/node1/cpu5

 

quoted

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.

If there are multiple fake nodes on a real physical node, all cpus in that 
node should appear in the cpulist for each fake node for which it has 
local distance.

Currently, the behavior of fake numa is not so on x86 as well? Below is
a sample output from a single node x86 system booted with numa=fake=8:

# cat node0/cpulist

# cat node1/cpulist

...
# cat node6/cpulist

# cat node7/cpulist
0-7

Presently, just fixing the cpu association issue with ppc, as explained
in my previous mail.

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

On Wed, 2 Sep 2009, Ankita Garg wrote:

Currently, the behavior of fake numa is not so on x86 as well? Below is
a sample output from a single node x86 system booted with numa=fake=8:

# cat node0/cpulist

# cat node1/cpulist

...
# cat node6/cpulist

# cat node7/cpulist
0-7

Presently, just fixing the cpu association issue with ppc, as explained
in my previous mail.

Right, I'm proposing an alternate mapping scheme (which we've used for 
years) for both platforms such that a cpu is bound (and is set in 
cpumask_of_node()) to each fake node with which it has physical affinity.  
That is the only way for zonelist ordering in node order, task migration 
from offlined cpus, correct sched domains, etc.  I can propose a patchset 
for x86_64 to do exactly this if there aren't any objections and I hope 
you'll help do ppc.

On Thu, Sep 3, 2009 at 1:06 AM, David Rientjes[off-list ref] wrote:

On Wed, 2 Sep 2009, Ankita Garg wrote:

quoted

Currently, the behavior of fake numa is not so on x86 as well? Below is
a sample output from a single node x86 system booted with numa=3Dfake=3D=

8:

quoted

# cat node0/cpulist

# cat node1/cpulist

...
# cat node6/cpulist

# cat node7/cpulist
0-7

Presently, just fixing the cpu association issue with ppc, as explained
in my previous mail.

Right, I'm proposing an alternate mapping scheme (which we've used for
years) for both platforms such that a cpu is bound (and is set in
cpumask_of_node()) to each fake node with which it has physical affinity.
That is the only way for zonelist ordering in node order, task migration
from offlined cpus, correct sched domains, etc. =A0I can propose a patchs=

et

for x86_64 to do exactly this if there aren't any objections and I hope
you'll help do ppc.

Sounds interesting, I'd definitely be interested in seeing your
proposal, but I would think of that as additional development on top
of this patch

Balbir Singh.

On Thu, 3 Sep 2009, Balbir Singh wrote:

quoted

Right, I'm proposing an alternate mapping scheme (which we've used for
years) for both platforms such that a cpu is bound (and is set in
cpumask_of_node()) to each fake node with which it has physical affinity.
That is the only way for zonelist ordering in node order, task migration
from offlined cpus, correct sched domains, etc.  I can propose a patchset
for x86_64 to do exactly this if there aren't any objections and I hope
you'll help do ppc.

Sounds interesting, I'd definitely be interested in seeing your
proposal, but I would think of that as additional development on top
of this patch

Absolutely.  I'm not familiar with numa=fake on ppc, but if cpus are being 
bound to nodes with which they don't have affinity, it definitely warrants 
a fix such as this (although the initial value for fake_enabled looks 
wrong and fake_numa_node_mapping[] can be __cpuinitdata).  I'll cc you, 
Ben, and Ankita on the x86_64 patches.  Thanks.