Subject: Re: [PATCH] Fix fake numa on ppc

From: Ankita Garg <[email-masked]>
Date: Wed, 2 Sep 2009 11:06:53 +0530

Hi Balbir,

On Tue, Sep 01, 2009 at 07:57:29PM +0530, Balbir Singh wrote:
> * Ankita Garg <[email-masked]> [2009-09-01 14:54:07]:
> 
> > Hi Balbir,
> > 
> > On Tue, Sep 01, 2009 at 11:27:53AM +0530, Balbir Singh wrote:
> > > * Ankita Garg <[email-masked]> [2009-09-01 10:33:16]:
> > > 
> > > > 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.
> > > >
> > > 
> > > Some details on how you tested it and results before and after would
> > > be nice. Please see git commit 1daa6d08d1257aa61f376c3cc4795660877fb9e3
> > > for example
> > > 
> > >
> > 
> > Thanks for the quick review of the patch. Here is some information on
> > the testing:
> > 
> > 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
> > 
> 
> Oh! interesting.. cpuless nodes :) I think we need to fix this in the
> longer run and distribute cpus between fake numa nodes of a real node
> using some acceptable heuristic.
>

True. Presently this is broken on both x86 and ppc systems. It would be
interesting to find a way to map, for example, 4 cpus to >4 number of
fake nodes created from a single real numa node!
 
> > # cat /sys/devices/system/node/node4/cpulist
> > 4-7
> > 
> > > > 
> > > > Signed-off-by: Ankita Garg <[email-masked]>
> > > > 
> > > > 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 */
> > > 
> > > Coding style is broken
> > > 
> > 
> > Fixed.
> > 
> > > > +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;
> > > 
> > > Should we call this prev_nid?
> > > 
> > 
> > Yes, makes sense.
> > > >  	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) {
> > > 
> > > OK, so this is called when the real NUMA node changes - comments would
> > > be nice
> > >
> > 
> > Thanks, have added the comment.
> > 
> > > > +			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;
> > > 
> > > Have you tried passing just numa=fake= without any commandline?
> > > That should enable fake_enabled, but I wonder if that negatively
> > > impacts numa_setup_cpu(). I wonder if you should look at cmdline
> > > to decide on fake_enabled.
> > >
> > 
> > fake_enabled does get set even for numa=fake=. However, it does not
> > impact numa_setup_cpu, since fake_numa_node_mapping array would have no
> > mapping stored and there is a condition there already to check for the
> > value of the mapping. I confirmed this by booting with the above
> > parameter as well.
> > 
> > > > +	}
> > > > 
> > > >  	return 0;
> > > >  }
> > > >
> > > 
> > > Overall, I think this is the right thing to do, we need to move in
> > > this direction. 
> > > 
> > 
> > Heres the updated patch:
> > 
> > Signed-off-by: Ankita Garg <[email-masked]> 
> > 
> > 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;
> >  }
> >
> 
> 
> Looks good to me
> 
> 
> Reviewed-by: Balbir Singh <[email-masked]>
> 
> 
> 
> -- 
> 	Balbir

-- 
Regards,
Ankita Garg ([email-masked])
Linux Technology Center
IBM India Systems & Technology Labs, 
Bangalore, India