Patchwork [v2] Fix fake numa on ppc

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Submitter Ankita Garg
Date Sept. 2, 2009, 6:09 a.m.
Message ID <20090902060911.GA5728@in.ibm.com>
Download mbox | patch
Permalink /patch/32814/
State Deferred
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Ankita Garg - Sept. 2, 2009, 6:09 a.m.
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
David Rientjes - Sept. 2, 2009, 6:37 a.m.
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.
Ankita Garg - Sept. 2, 2009, 8:03 a.m.
Hi David,

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

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

 
> > 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.
David Rientjes - Sept. 2, 2009, 7:36 p.m.
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.
Balbir Singh - Sept. 2, 2009, 7:56 p.m.
On Thu, Sep 3, 2009 at 1:06 AM, David Rientjes<rientjes@google.com> wrote:
> 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.

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.
David Rientjes - Sept. 2, 2009, 8:09 p.m.
On Thu, 3 Sep 2009, Balbir Singh wrote:

> > 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.

Patch

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 <ankita@in.ibm.com> 
Reviewed-by: Balbir Singh <balbir@linux.vnet.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 +26,13 @@ 
 #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;
 }