[PATCH 1/1] cpusets/sched_domain reconciliation

[PATCH 1/1] cpusets/sched_domain reconciliation

[Cliff Wickman]

Re-send of patch sent 8/23/2007, but refreshed for 2.6.23-rc5.

This patch reconciles cpusets and sched_domains that get out of sync
due to disabling and re-enabling cpu's.

This is still a problem in the 2.6.23-rc5 kernel.

Here is an example of how the problem can occur:

   system of cpu's   0 1 2 3 4 5
   create cpuset /x      2 3 4 5 
   create cpuset /x/y    2 3
   all cpusets are cpu_exclusive

   disable cpu 3
     x is now            2   4 5
     x/y is now          2
   enable cpu 3
     cpusets x and x/y are unchanged

   to restore the cpusets:
     echo 2-5 > /dev/cpuset/x
     echo 2-3 > /dev/cpuset/x/y

   At the first echo, which restores 3 to cpuset x, update_cpu_domains() is
   called for cpuset x/. 
   system of cpu's   0 1 2 3 4 5
   x is now              2 3 4 5
   x/y is now            2

   The system is partitioned between:
	its parent, the root cpuset, minus its child (x/ is 2-5): 0-1
        and x/ (2-5) , minus its child (x/y/ 2): 3-5

   The sched_domain's for parent 0-1 are updated.
   The sched_domain's for current 3-5 are updated.

   But 2 has been untouched.
   As a result, 3's SD points to sched_group_phys[3] which is the only
   sched_group_phys on 3's list.  It points to itself.
   But 2's SD points to sched_group_phys[2], which still points to
   sched_group_phys[3].
   When cpu 2 executes find_busiest_group() it will hang on the non-
   circular sched_group list.
           
cpuset.c:

This solution is to update the sched_domain's for the cpuset
whose cpu's were changed and, in addition, all its children.
Instead of calling update_cpu_domains(), call update_cpu_domains_tree(),
which calls update_cpu_domains() for every node from the one specified
down to all its children.

The extra sched_domain reconstruction is overhead, but only at the
frequency of administrative change to the cpusets.

There seems to be no administrative procedural work-around.  In the
example above one could not reverse the two echo's and set x/y before
x/.  It is not logical, so not allowed (Permission denied).

Thus the patch to cpuset.c makes the sched_domain's correct.

sched.c:

The patch to sched.c prevents the cpu hangs that otherwise occur
until the sched_domain's are made correct.

It puts checks into find_busiest_group() and find_idlest_group()
that break from their loops on a sched_group that points to itself.
This is needed because cpu's are going through load balancing before all
sched_domains have been reconstructed (see the example above).

This is admittedly a kludge. I leave it to the scheduler gurus to recommend
a better way update the sched_domains or to keep cpus out of the
sched_domains while they are being reconstructed.

Diffed against 2.6.23-rc5

Signed-off-by: Cliff Wickman <cpw@sgi.com>

---
 kernel/cpuset.c |   43 +++++++++++++++++++++++++++++++++++++++----
 kernel/sched.c  |   18 ++++++++++++++----
 2 files changed, 53 insertions(+), 8 deletions(-)

Index: p1/kernel/sched.c
===================================================================
--- p1.orig/kernel/sched.c
+++ p1/kernel/sched.c
@@ -1219,11 +1219,14 @@ static inline unsigned long cpu_avg_load
 static struct sched_group *
 find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
 {
-	struct sched_group *idlest = NULL, *this = NULL, *group = sd->groups;
+	struct sched_group *idlest = NULL, *this = sd->groups, *group = sd->groups;
+	struct sched_group *self, *prev;
 	unsigned long min_load = ULONG_MAX, this_load = 0;
 	int load_idx = sd->forkexec_idx;
 	int imbalance = 100 + (sd->imbalance_pct-100)/2;
 
+	prev = group;
+	self = group;
 	do {
 		unsigned long load, avg_load;
 		int local_group;
@@ -1260,8 +1263,10 @@ find_idlest_group(struct sched_domain *s
 			idlest = group;
 		}
 nextgroup:
+		prev = self;
+		self = group;
 		group = group->next;
-	} while (group != sd->groups);
+	} while (group != sd->groups && group != self && group != prev);
 
 	if (!idlest || 100*this_load < imbalance*min_load)
 		return NULL;
@@ -2306,7 +2311,8 @@ find_busiest_group(struct sched_domain *
 		   unsigned long *imbalance, enum cpu_idle_type idle,
 		   int *sd_idle, cpumask_t *cpus, int *balance)
 {
-	struct sched_group *busiest = NULL, *this = NULL, *group = sd->groups;
+	struct sched_group *busiest = NULL, *this = sd->groups, *group = sd->groups;
+	struct sched_group *self, *prev;
 	unsigned long max_load, avg_load, total_load, this_load, total_pwr;
 	unsigned long max_pull;
 	unsigned long busiest_load_per_task, busiest_nr_running;
@@ -2329,6 +2335,8 @@ find_busiest_group(struct sched_domain *
 	else
 		load_idx = sd->idle_idx;
 
+	prev = group;
+	self = group;
 	do {
 		unsigned long load, group_capacity;
 		int local_group;
@@ -2461,8 +2469,10 @@ find_busiest_group(struct sched_domain *
 		}
 group_next:
 #endif
+		prev = self;
+		self = group;
 		group = group->next;
-	} while (group != sd->groups);
+	} while (group != sd->groups && group != self && group != prev);
 
 	if (!busiest || this_load >= max_load || busiest_nr_running == 0)
 		goto out_balanced;
Index: p1/kernel/cpuset.c
===================================================================
--- p1.orig/kernel/cpuset.c
+++ p1/kernel/cpuset.c
@@ -52,6 +52,7 @@
 #include <asm/uaccess.h>
 #include <asm/atomic.h>
 #include <linux/mutex.h>
+#include <linux/kfifo.h>
 
 #define CPUSET_SUPER_MAGIC		0x27e0eb
 
@@ -789,8 +790,8 @@ static void update_cpu_domains(struct cp
 			return;
 		cspan = CPU_MASK_NONE;
 	} else {
-		if (cpus_empty(pspan))
-			return;
+		/* parent may be empty, but update anyway */
+
 		cspan = cur->cpus_allowed;
 		/*
 		 * Get all cpus from current cpuset's cpus_allowed not part
@@ -808,6 +809,40 @@ static void update_cpu_domains(struct cp
 }
 
 /*
+ * Call update_cpu_domains for cpuset "cur", and for all of its children.
+ *
+ * This walk processes the tree from top to bottom, completing one layer
+ * before dropping down to the next.  It always processes a node before
+ * any of its children.
+ *
+ * Call with manage_mutex held.
+ * Must not be called holding callback_mutex, because we must
+ * not call lock_cpu_hotplug() while holding callback_mutex.
+ */
+static void
+update_cpu_domains_tree(struct cpuset *root)
+{
+	struct cpuset *cp;	/* scans cpusets being updated */
+	struct cpuset *child;	/* scans child cpusets of cp */
+	struct kfifo *queue;	/* fifo queue of cpusets to be updated */
+
+	queue = kfifo_alloc(number_of_cpusets * sizeof(cp), GFP_KERNEL, NULL);
+	if (queue == ERR_PTR(-ENOMEM))
+		return;
+
+	__kfifo_put(queue, (unsigned char *)&root, sizeof(root));
+
+	while (__kfifo_get(queue, (unsigned char *)&cp, sizeof(cp))) {
+		list_for_each_entry(child, &cp->children, sibling)
+		    __kfifo_put(queue,(unsigned char *)&child,sizeof(child));
+		update_cpu_domains(cp);
+	}
+
+	kfifo_free(queue);
+	return;
+}
+
+/*
  * Call with manage_mutex held.  May take callback_mutex during call.
  */
 
@@ -846,7 +881,7 @@ static int update_cpumask(struct cpuset 
 	cs->cpus_allowed = trialcs.cpus_allowed;
 	mutex_unlock(&callback_mutex);
 	if (is_cpu_exclusive(cs) && !cpus_unchanged)
-		update_cpu_domains(cs);
+		update_cpu_domains_tree(cs);
 	return 0;
 }
 
@@ -1087,7 +1122,7 @@ static int update_flag(cpuset_flagbits_t
 	mutex_unlock(&callback_mutex);
 
 	if (cpu_exclusive_changed)
-                update_cpu_domains(cs);
+                update_cpu_domains_tree(cs);
 	return 0;
 }
 

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Re: [PATCH 1/1] cpusets/sched_domain reconciliation

[Nick Piggin]

On Friday 14 September 2007 08:46, Andrew Morton wrote:
> On Fri, 07 Sep 2007 16:07:04 -0500
>
> cpw@sgi.com (Cliff Wickman) wrote:
> > Re-send of patch sent 8/23/2007, but refreshed for 2.6.23-rc5.
> >
> > This patch reconciles cpusets and sched_domains that get out of sync
> > due to disabling and re-enabling cpu's.
> >
> > This is still a problem in the 2.6.23-rc5 kernel.
> >
> > Here is an example of how the problem can occur:
> >
> >    system of cpu's   0 1 2 3 4 5
> >    create cpuset /x      2 3 4 5
> >    create cpuset /x/y    2 3
> >    all cpusets are cpu_exclusive
> >
> >    disable cpu 3
> >      x is now            2   4 5
> >      x/y is now          2
> >    enable cpu 3
> >      cpusets x and x/y are unchanged
> >
> >    to restore the cpusets:
> >      echo 2-5 > /dev/cpuset/x
> >      echo 2-3 > /dev/cpuset/x/y
> >
> >    At the first echo, which restores 3 to cpuset x, update_cpu_domains()
> > is called for cpuset x/.
> >    system of cpu's   0 1 2 3 4 5
> >    x is now              2 3 4 5
> >    x/y is now            2
> >
> >    The system is partitioned between:
> > 	its parent, the root cpuset, minus its child (x/ is 2-5): 0-1
> >         and x/ (2-5) , minus its child (x/y/ 2): 3-5
> >
> >    The sched_domain's for parent 0-1 are updated.
> >    The sched_domain's for current 3-5 are updated.
> >
> >    But 2 has been untouched.
> >    As a result, 3's SD points to sched_group_phys[3] which is the only
> >    sched_group_phys on 3's list.  It points to itself.
> >    But 2's SD points to sched_group_phys[2], which still points to
> >    sched_group_phys[3].
> >    When cpu 2 executes find_busiest_group() it will hang on the non-
> >    circular sched_group list.
> >
> > cpuset.c:
> >
> > This solution is to update the sched_domain's for the cpuset
> > whose cpu's were changed and, in addition, all its children.
> > Instead of calling update_cpu_domains(), call update_cpu_domains_tree(),
> > which calls update_cpu_domains() for every node from the one specified
> > down to all its children.
> >
> > The extra sched_domain reconstruction is overhead, but only at the
> > frequency of administrative change to the cpusets.
> >
> > There seems to be no administrative procedural work-around.  In the
> > example above one could not reverse the two echo's and set x/y before
> > x/.  It is not logical, so not allowed (Permission denied).
> >
> > Thus the patch to cpuset.c makes the sched_domain's correct.
> >
> > sched.c:
> >
> > The patch to sched.c prevents the cpu hangs that otherwise occur
> > until the sched_domain's are made correct.
> >
> > It puts checks into find_busiest_group() and find_idlest_group()
> > that break from their loops on a sched_group that points to itself.
> > This is needed because cpu's are going through load balancing before all
> > sched_domains have been reconstructed (see the example above).
> >
> > This is admittedly a kludge. I leave it to the scheduler gurus to
> > recommend a better way update the sched_domains or to keep cpus out of
> > the sched_domains while they are being reconstructed.
>
> You should cc scheduler gurus when hoping things about them ;)
>
> I suspect your change is fundamentally incompatible with, and perhaps
> obsoleted by
> ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc4/2.
>6.23-rc4-mm1/broken-out/cpuset-remove-sched-domain-hooks-from-cpusets.patch
>
> Problem is, cpuset-remove-sched-domain-hooks-from-cpusets.patch has been
> hanging around in -mm for a year while Paul makes up his mind about it.
>
> Can we please get all this sorted out??

cpus_exclusive is supposed to partition the system (like a dynamically
configurable isolcpus=). However the exact semantics of it IIRC are
defined such that it is pretty well unusable.

IIRC I have a patch that converts it to sane semantics and does
opportunistic sched domains partitioning and of course fixes the hotplug
issue as well... but Paul didn't like it for some reason.

Anyway, until there is some very clear semantic for what cpus_exclusive
does, then it is silly to retain the broken sched-domains code. I don't know
why that patch isn't merged, but it should be... (I thought it was when this
last came up ages ago).

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Re: [PATCH 1/1] cpusets/sched_domain reconciliation

[Andrew Morton]

On Fri, 07 Sep 2007 16:07:04 -0500
cpw@sgi.com (Cliff Wickman) wrote:

> 
> 
> 
> Re-send of patch sent 8/23/2007, but refreshed for 2.6.23-rc5.
> 
> This patch reconciles cpusets and sched_domains that get out of sync
> due to disabling and re-enabling cpu's.
> 
> This is still a problem in the 2.6.23-rc5 kernel.
> 
> Here is an example of how the problem can occur:
> 
>    system of cpu's   0 1 2 3 4 5
>    create cpuset /x      2 3 4 5 
>    create cpuset /x/y    2 3
>    all cpusets are cpu_exclusive
> 
>    disable cpu 3
>      x is now            2   4 5
>      x/y is now          2
>    enable cpu 3
>      cpusets x and x/y are unchanged
> 
>    to restore the cpusets:
>      echo 2-5 > /dev/cpuset/x
>      echo 2-3 > /dev/cpuset/x/y
> 
>    At the first echo, which restores 3 to cpuset x, update_cpu_domains() is
>    called for cpuset x/. 
>    system of cpu's   0 1 2 3 4 5
>    x is now              2 3 4 5
>    x/y is now            2
> 
>    The system is partitioned between:
> 	its parent, the root cpuset, minus its child (x/ is 2-5): 0-1
>         and x/ (2-5) , minus its child (x/y/ 2): 3-5
> 
>    The sched_domain's for parent 0-1 are updated.
>    The sched_domain's for current 3-5 are updated.
> 
>    But 2 has been untouched.
>    As a result, 3's SD points to sched_group_phys[3] which is the only
>    sched_group_phys on 3's list.  It points to itself.
>    But 2's SD points to sched_group_phys[2], which still points to
>    sched_group_phys[3].
>    When cpu 2 executes find_busiest_group() it will hang on the non-
>    circular sched_group list.
>            
> cpuset.c:
> 
> This solution is to update the sched_domain's for the cpuset
> whose cpu's were changed and, in addition, all its children.
> Instead of calling update_cpu_domains(), call update_cpu_domains_tree(),
> which calls update_cpu_domains() for every node from the one specified
> down to all its children.
> 
> The extra sched_domain reconstruction is overhead, but only at the
> frequency of administrative change to the cpusets.
> 
> There seems to be no administrative procedural work-around.  In the
> example above one could not reverse the two echo's and set x/y before
> x/.  It is not logical, so not allowed (Permission denied).
> 
> Thus the patch to cpuset.c makes the sched_domain's correct.
> 
> sched.c:
> 
> The patch to sched.c prevents the cpu hangs that otherwise occur
> until the sched_domain's are made correct.
> 
> It puts checks into find_busiest_group() and find_idlest_group()
> that break from their loops on a sched_group that points to itself.
> This is needed because cpu's are going through load balancing before all
> sched_domains have been reconstructed (see the example above).
> 
> This is admittedly a kludge. I leave it to the scheduler gurus to recommend
> a better way update the sched_domains or to keep cpus out of the
> sched_domains while they are being reconstructed.
> 

You should cc scheduler gurus when hoping things about them ;)

I suspect your change is fundamentally incompatible with, and perhaps
obsoleted by
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc4/2.6.23-rc4-mm1/broken-out/cpuset-remove-sched-domain-hooks-from-cpusets.patch

Problem is, cpuset-remove-sched-domain-hooks-from-cpusets.patch has been
hanging around in -mm for a year while Paul makes up his mind about it.

Can we please get all this sorted out??

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Re: [PATCH 1/1] cpusets/sched_domain reconciliation

[Paul Mundt]

On Thu, Sep 13, 2007 at 03:46:07PM -0700, Andrew Morton wrote:
> On Fri, 07 Sep 2007 16:07:04 -0500
> cpw@sgi.com (Cliff Wickman) wrote:
> > Thus the patch to cpuset.c makes the sched_domain's correct.
> 
> You should cc scheduler gurus when hoping things about them ;)
> 
> I suspect your change is fundamentally incompatible with, and perhaps
> obsoleted by
> ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc4/2.6.23-rc4-mm1/broken-out/cpuset-remove-sched-domain-hooks-from-cpusets.patch
> 
> Problem is, cpuset-remove-sched-domain-hooks-from-cpusets.patch has been
> hanging around in -mm for a year while Paul makes up his mind about it.
> 
> Can we please get all this sorted out??
> 
Note that removing the scheduler domain hooks also fixes up the build for
cpusets on UP NUMA. If this patch isn't going to go in, the other
alternative is simply to stub out scheduler domains there.

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Re: [PATCH 1/1] cpusets/sched_domain reconciliation

[Paul Jackson]

Andrew replied to Cliff a few days ago:
> I suspect your change is fundamentally incompatible with, and perhaps
> obsoleted by ... cpuset-remove-sched-domain-hooks-from-cpusets.patch

I suspect the same thing.

> Problem is, cpuset-remove-sched-domain-hooks-from-cpusets.patch has been
> hanging around in -mm for a year while Paul makes up his mind about it.
> 
> Can we please get all this sorted out??

I'll see what I can do.  Cpuset support seems to have finally gotten
back to the front of my queue.

Sorry for the absurdly long hiatus.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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[PATCH 1/1] cpusets/sched_domain reconciliation

[Cliff Wickman]

This patch reconciles cpusets and sched_domains that get out of sync
due to disabling and re-enabling cpu's.

This is still a problem in the 2.6.23-rc3 kernel.  (and also 2.6.22)

Here is an example of how the problem can occur:

   system of cpu's   0 1 2 3 4 5
   create cpuset /x      2 3 4 5 
   create cpuset /x/y    2 3
   all cpusets are cpu_exclusive

   disable cpu 3
     x is now            2   4 5
     x/y is now          2
   enable cpu 3
     cpusets x and x/y are unchanged

   to restore the cpusets:
     echo 2-5 > /dev/cpuset/x
     echo 2-3 > /dev/cpuset/x/y

   At the first echo, which restores 3 to cpuset x, update_cpu_domains() is
   called for cpuset x/. 
   system of cpu's   0 1 2 3 4 5
   x is now              2 3 4 5
   x/y is now            2

   The system is partitioned between:
	its parent, the root cpuset, minus its child (x/ is 2-5): 0-1
        and x/ (2-5) , minus its child (x/y/ 2): 3-5

   The sched_domain's for parent 0-1 are updated.
   The sched_domain's for current 3-5 are updated.

   But 2 has been untouched.
   As a result, 3's SD points to sched_group_phys[3] which is the only
   sched_group_phys on 3's list.  It points to itself.
   But 2's SD points to sched_group_phys[2], which still points to
   sched_group_phys[3].
   When cpu 2 executes find_busiest_group() it will hang on the non-
   circular sched_group list.
           
cpuset.c:

This solution is to update the sched_domain's for the cpuset
whose cpu's were changed and, in addition, all its children.
Instead of calling update_cpu_domains(), call update_cpu_domains_tree(),
which calls update_cpu_domains() for every node from the one specified
down to all its children.

The extra sched_domain reconstruction is overhead, but only at the
frequency of administrative change to the cpusets.

There seems to be no administrative procedural work-around.  In the
example above one could not reverse the two echo's and set x/y before
x/.  It is not logical, so not allowed (Permission denied).

Thus the patch to cpuset.c makes the sched_domain's correct.

sched.c:

The patch to sched.c prevents the cpu hangs that otherwise occur
until the sched_domain's are made correct.

It puts checks into find_busiest_group() and find_idlest_group()
that break from their loops on a sched_group that points to itself.
This is needed because cpu's are going through load balancing before all
sched_domains have been reconstructed (see the example above).

This is admittedly a kludge. I leave it to the scheduler gurus to recommend
a better way to keep cpus out of the sched_domains while they are
being reconstructed.

Diffed against 2.6.23-rc3

Signed-off-by: Cliff Wickman <cpw@sgi.com>

---
 kernel/cpuset.c |   43 +++++++++++++++++++++++++++++++++++++++----
 kernel/sched.c  |   18 ++++++++++++++----
 2 files changed, 53 insertions(+), 8 deletions(-)

Index: linus.070821/kernel/sched.c
===================================================================
--- linus.070821.orig/kernel/sched.c
+++ linus.070821/kernel/sched.c
@@ -1196,11 +1196,14 @@ static inline unsigned long cpu_avg_load
 static struct sched_group *
 find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
 {
-	struct sched_group *idlest = NULL, *this = NULL, *group = sd->groups;
+	struct sched_group *idlest = NULL, *this = sd->groups, *group = sd->groups;
+	struct sched_group *self, *prev;
 	unsigned long min_load = ULONG_MAX, this_load = 0;
 	int load_idx = sd->forkexec_idx;
 	int imbalance = 100 + (sd->imbalance_pct-100)/2;
 
+	prev = group;
+	self = group;
 	do {
 		unsigned long load, avg_load;
 		int local_group;
@@ -1237,8 +1240,10 @@ find_idlest_group(struct sched_domain *s
 			idlest = group;
 		}
 nextgroup:
+		prev = self;
+		self = group;
 		group = group->next;
-	} while (group != sd->groups);
+	} while (group != sd->groups && group != self && group != prev);
 
 	if (!idlest || 100*this_load < imbalance*min_load)
 		return NULL;
@@ -2288,7 +2293,8 @@ find_busiest_group(struct sched_domain *
 		   unsigned long *imbalance, enum cpu_idle_type idle,
 		   int *sd_idle, cpumask_t *cpus, int *balance)
 {
-	struct sched_group *busiest = NULL, *this = NULL, *group = sd->groups;
+	struct sched_group *busiest = NULL, *this = sd->groups, *group = sd->groups;
+	struct sched_group *self, *prev;
 	unsigned long max_load, avg_load, total_load, this_load, total_pwr;
 	unsigned long max_pull;
 	unsigned long busiest_load_per_task, busiest_nr_running;
@@ -2311,6 +2317,8 @@ find_busiest_group(struct sched_domain *
 	else
 		load_idx = sd->idle_idx;
 
+	prev = group;
+	self = group;
 	do {
 		unsigned long load, group_capacity;
 		int local_group;
@@ -2443,8 +2451,10 @@ find_busiest_group(struct sched_domain *
 		}
 group_next:
 #endif
+		prev = self;
+		self = group;
 		group = group->next;
-	} while (group != sd->groups);
+	} while (group != sd->groups && group != self && group != prev);
 
 	if (!busiest || this_load >= max_load || busiest_nr_running == 0)
 		goto out_balanced;
Index: linus.070821/kernel/cpuset.c
===================================================================
--- linus.070821.orig/kernel/cpuset.c
+++ linus.070821/kernel/cpuset.c
@@ -52,6 +52,7 @@
 #include <asm/uaccess.h>
 #include <asm/atomic.h>
 #include <linux/mutex.h>
+#include <linux/kfifo.h>
 
 #define CPUSET_SUPER_MAGIC		0x27e0eb
 
@@ -789,8 +790,8 @@ static void update_cpu_domains(struct cp
 			return;
 		cspan = CPU_MASK_NONE;
 	} else {
-		if (cpus_empty(pspan))
-			return;
+		/* parent may be empty, but update anyway */
+
 		cspan = cur->cpus_allowed;
 		/*
 		 * Get all cpus from current cpuset's cpus_allowed not part
@@ -808,6 +809,40 @@ static void update_cpu_domains(struct cp
 }
 
 /*
+ * Call update_cpu_domains for cpuset "cur", and for all of its children.
+ *
+ * This walk processes the tree from top to bottom, completing one layer
+ * before dropping down to the next.  It always processes a node before
+ * any of its children.
+ *
+ * Call with manage_mutex held.
+ * Must not be called holding callback_mutex, because we must
+ * not call lock_cpu_hotplug() while holding callback_mutex.
+ */
+static void
+update_cpu_domains_tree(struct cpuset *root)
+{
+	struct cpuset *cp;	/* scans cpusets being updated */
+	struct cpuset *child;	/* scans child cpusets of cp */
+	struct kfifo *queue;	/* fifo queue of cpusets to be updated */
+
+	queue = kfifo_alloc(number_of_cpusets * sizeof(cp), GFP_KERNEL, NULL);
+	if (queue == ERR_PTR(-ENOMEM))
+		return;
+
+	__kfifo_put(queue, (unsigned char *)&root, sizeof(root));
+
+	while (__kfifo_get(queue, (unsigned char *)&cp, sizeof(cp))) {
+		list_for_each_entry(child, &cp->children, sibling)
+		    __kfifo_put(queue,(unsigned char *)&child,sizeof(child));
+		update_cpu_domains(cp);
+	}
+
+	kfifo_free(queue);
+	return;
+}
+
+/*
  * Call with manage_mutex held.  May take callback_mutex during call.
  */
 
@@ -846,7 +881,7 @@ static int update_cpumask(struct cpuset 
 	cs->cpus_allowed = trialcs.cpus_allowed;
 	mutex_unlock(&callback_mutex);
 	if (is_cpu_exclusive(cs) && !cpus_unchanged)
-		update_cpu_domains(cs);
+		update_cpu_domains_tree(cs);
 	return 0;
 }
 
@@ -1087,7 +1122,7 @@ static int update_flag(cpuset_flagbits_t
 	mutex_unlock(&callback_mutex);
 
 	if (cpu_exclusive_changed)
-                update_cpu_domains(cs);
+                update_cpu_domains_tree(cs);
 	return 0;
 }
 
-- 
Cliff Wickman
Silicon Graphics, Inc.
cpw@sgi.com
(651) 683-3824

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