4 files changed, 492 insertions, 21 deletions

diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 85eeab5e7e32..141bef1c8599 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -19,7 +19,8 @@ CONTENTS:
   1.4 What are exclusive cpusets ?
   1.5 What is memory_pressure ?
   1.6 What is memory spread ?
-  1.7 How do I use cpusets ?
+  1.7 What is sched_load_balance ?
+  1.8 How do I use cpusets ?
 2. Usage Examples and Syntax
   2.1 Basic Usage
   2.2 Adding/removing cpus
@@ -359,8 +360,144 @@ policy, especially for jobs that might have one thread reading in the
 data set, the memory allocation across the nodes in the jobs cpuset
 can become very uneven.
 
+1.7 What is sched_load_balance ?
+--------------------------------
 
-1.7 How do I use cpusets ?
+The kernel scheduler (kernel/sched.c) automatically load balances
+tasks.  If one CPU is underutilized, kernel code running on that
+CPU will look for tasks on other more overloaded CPUs and move those
+tasks to itself, within the constraints of such placement mechanisms
+as cpusets and sched_setaffinity.
+
+The algorithmic cost of load balancing and its impact on key shared
+kernel data structures such as the task list increases more than
+linearly with the number of CPUs being balanced.  So the scheduler
+has support to  partition the systems CPUs into a number of sched
+domains such that it only load balances within each sched domain.
+Each sched domain covers some subset of the CPUs in the system;
+no two sched domains overlap; some CPUs might not be in any sched
+domain and hence won't be load balanced.
+
+Put simply, it costs less to balance between two smaller sched domains
+than one big one, but doing so means that overloads in one of the
+two domains won't be load balanced to the other one.
+
+By default, there is one sched domain covering all CPUs, except those
+marked isolated using the kernel boot time "isolcpus=" argument.
+
+This default load balancing across all CPUs is not well suited for
+the following two situations:
+ 1) On large systems, load balancing across many CPUs is expensive.
+    If the system is managed using cpusets to place independent jobs
+    on separate sets of CPUs, full load balancing is unnecessary.
+ 2) Systems supporting realtime on some CPUs need to minimize
+    system overhead on those CPUs, including avoiding task load
+    balancing if that is not needed.
+
+When the per-cpuset flag "sched_load_balance" is enabled (the default
+setting), it requests that all the CPUs in that cpusets allowed 'cpus'
+be contained in a single sched domain, ensuring that load balancing
+can move a task (not otherwised pinned, as by sched_setaffinity)
+from any CPU in that cpuset to any other.
+
+When the per-cpuset flag "sched_load_balance" is disabled, then the
+scheduler will avoid load balancing across the CPUs in that cpuset,
+--except-- in so far as is necessary because some overlapping cpuset
+has "sched_load_balance" enabled.
+
+So, for example, if the top cpuset has the flag "sched_load_balance"
+enabled, then the scheduler will have one sched domain covering all
+CPUs, and the setting of the "sched_load_balance" flag in any other
+cpusets won't matter, as we're already fully load balancing.
+
+Therefore in the above two situations, the top cpuset flag
+"sched_load_balance" should be disabled, and only some of the smaller,
+child cpusets have this flag enabled.
+
+When doing this, you don't usually want to leave any unpinned tasks in
+the top cpuset that might use non-trivial amounts of CPU, as such tasks
+may be artificially constrained to some subset of CPUs, depending on
+the particulars of this flag setting in descendent cpusets.  Even if
+such a task could use spare CPU cycles in some other CPUs, the kernel
+scheduler might not consider the possibility of load balancing that
+task to that underused CPU.
+
+Of course, tasks pinned to a particular CPU can be left in a cpuset
+that disables "sched_load_balance" as those tasks aren't going anywhere
+else anyway.
+
+There is an impedance mismatch here, between cpusets and sched domains.
+Cpusets are hierarchical and nest.  Sched domains are flat; they don't
+overlap and each CPU is in at most one sched domain.
+
+It is necessary for sched domains to be flat because load balancing
+across partially overlapping sets of CPUs would risk unstable dynamics
+that would be beyond our understanding.  So if each of two partially
+overlapping cpusets enables the flag 'sched_load_balance', then we
+form a single sched domain that is a superset of both.  We won't move
+a task to a CPU outside it cpuset, but the scheduler load balancing
+code might waste some compute cycles considering that possibility.
+
+This mismatch is why there is not a simple one-to-one relation
+between which cpusets have the flag "sched_load_balance" enabled,
+and the sched domain configuration.  If a cpuset enables the flag, it
+will get balancing across all its CPUs, but if it disables the flag,
+it will only be assured of no load balancing if no other overlapping
+cpuset enables the flag.
+
+If two cpusets have partially overlapping 'cpus' allowed, and only
+one of them has this flag enabled, then the other may find its
+tasks only partially load balanced, just on the overlapping CPUs.
+This is just the general case of the top_cpuset example given a few
+paragraphs above.  In the general case, as in the top cpuset case,
+don't leave tasks that might use non-trivial amounts of CPU in
+such partially load balanced cpusets, as they may be artificially
+constrained to some subset of the CPUs allowed to them, for lack of
+load balancing to the other CPUs.
+
+1.7.1 sched_load_balance implementation details.
+------------------------------------------------
+
+The per-cpuset flag 'sched_load_balance' defaults to enabled (contrary
+to most cpuset flags.)  When enabled for a cpuset, the kernel will
+ensure that it can load balance across all the CPUs in that cpuset
+(makes sure that all the CPUs in the cpus_allowed of that cpuset are
+in the same sched domain.)
+
+If two overlapping cpusets both have 'sched_load_balance' enabled,
+then they will be (must be) both in the same sched domain.
+
+If, as is the default, the top cpuset has 'sched_load_balance' enabled,
+then by the above that means there is a single sched domain covering
+the whole system, regardless of any other cpuset settings.
+
+The kernel commits to user space that it will avoid load balancing
+where it can.  It will pick as fine a granularity partition of sched
+domains as it can while still providing load balancing for any set
+of CPUs allowed to a cpuset having 'sched_load_balance' enabled.
+
+The internal kernel cpuset to scheduler interface passes from the
+cpuset code to the scheduler code a partition of the load balanced
+CPUs in the system. This partition is a set of subsets (represented
+as an array of cpumask_t) of CPUs, pairwise disjoint, that cover all
+the CPUs that must be load balanced.
+
+Whenever the 'sched_load_balance' flag changes, or CPUs come or go
+from a cpuset with this flag enabled, or a cpuset with this flag
+enabled is removed, the cpuset code builds a new such partition and
+passes it to the scheduler sched domain setup code, to have the sched
+domains rebuilt as necessary.
+
+This partition exactly defines what sched domains the scheduler should
+setup - one sched domain for each element (cpumask_t) in the partition.
+
+The scheduler remembers the currently active sched domain partitions.
+When the scheduler routine partition_sched_domains() is invoked from
+the cpuset code to update these sched domains, it compares the new
+partition requested with the current, and updates its sched domains,
+removing the old and adding the new, for each change.
+
+1.8 How do I use cpusets ?
 --------------------------
 
 In order to minimize the impact of cpusets on critical kernel
diff --git a/include/linux/sched.h b/include/linux/sched.h
index cbd8731a66e6..4bbbe12880d7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -737,6 +737,8 @@ struct sched_domain {
 #endif
 };
 
+extern void partition_sched_domains(int ndoms_new, cpumask_t *doms_new);
+
 #endif  /* CONFIG_SMP */
 
 /*
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 1133062395e2..203ca52e78dd 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -4,7 +4,7 @@
  *  Processor and Memory placement constraints for sets of tasks.
  *
  *  Copyright (C) 2003 BULL SA.
- *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
+ *  Copyright (C) 2004-2007 Silicon Graphics, Inc.
  *  Copyright (C) 2006 Google, Inc
  *
  *  Portions derived from Patrick Mochel's sysfs code.
@@ -54,6 +54,7 @@
 #include <asm/uaccess.h>
 #include <asm/atomic.h>
 #include <linux/mutex.h>
+#include <linux/kfifo.h>
 
 /*
  * Tracks how many cpusets are currently defined in system.
@@ -91,6 +92,9 @@ struct cpuset {
         int mems_generation;
 
         struct fmeter fmeter;           /* memory_pressure filter */
+
+        /* partition number for rebuild_sched_domains() */
+        int pn;
 };
 
 /* Retrieve the cpuset for a cgroup */
@@ -113,6 +117,7 @@ typedef enum {
         CS_CPU_EXCLUSIVE,
         CS_MEM_EXCLUSIVE,
         CS_MEMORY_MIGRATE,
+        CS_SCHED_LOAD_BALANCE,
         CS_SPREAD_PAGE,
         CS_SPREAD_SLAB,
 } cpuset_flagbits_t;
@@ -128,6 +133,11 @@ static inline int is_mem_exclusive(const struct cpuset *cs)
         return test_bit(CS_MEM_EXCLUSIVE, &cs->flags);
 }
 
+static inline int is_sched_load_balance(const struct cpuset *cs)
+{
+        return test_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+}
+
 static inline int is_memory_migrate(const struct cpuset *cs)
 {
         return test_bit(CS_MEMORY_MIGRATE, &cs->flags);
@@ -482,6 +492,208 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
 }
 
 /*
+ * Helper routine for rebuild_sched_domains().
+ * Do cpusets a, b have overlapping cpus_allowed masks?
+ */
+
+static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
+{
+        return cpus_intersects(a->cpus_allowed, b->cpus_allowed);
+}
+
+/*
+ * rebuild_sched_domains()
+ *
+ * If the flag 'sched_load_balance' of any cpuset with non-empty
+ * 'cpus' changes, or if the 'cpus' allowed changes in any cpuset
+ * which has that flag enabled, or if any cpuset with a non-empty
+ * 'cpus' is removed, then call this routine to rebuild the
+ * scheduler's dynamic sched domains.
+ *
+ * This routine builds a partial partition of the systems CPUs
+ * (the set of non-overlappping cpumask_t's in the array 'part'
+ * below), and passes that partial partition to the kernel/sched.c
+ * partition_sched_domains() routine, which will rebuild the
+ * schedulers load balancing domains (sched domains) as specified
+ * by that partial partition.  A 'partial partition' is a set of
+ * non-overlapping subsets whose union is a subset of that set.
+ *
+ * See "What is sched_load_balance" in Documentation/cpusets.txt
+ * for a background explanation of this.
+ *
+ * Does not return errors, on the theory that the callers of this
+ * routine would rather not worry about failures to rebuild sched
+ * domains when operating in the severe memory shortage situations
+ * that could cause allocation failures below.
+ *
+ * Call with cgroup_mutex held.  May take callback_mutex during
+ * call due to the kfifo_alloc() and kmalloc() calls.  May nest
+ * a call to the lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
+ * Must not be called holding callback_mutex, because we must not
+ * call lock_cpu_hotplug() while holding callback_mutex.  Elsewhere
+ * the kernel nests callback_mutex inside lock_cpu_hotplug() calls.
+ * So the reverse nesting would risk an ABBA deadlock.
+ *
+ * The three key local variables below are:
+ *    q  - a kfifo queue of cpuset pointers, used to implement a
+ *         top-down scan of all cpusets.  This scan loads a pointer
+ *         to each cpuset marked is_sched_load_balance into the
+ *         array 'csa'.  For our purposes, rebuilding the schedulers
+ *         sched domains, we can ignore !is_sched_load_balance cpusets.
+ *  csa  - (for CpuSet Array) Array of pointers to all the cpusets
+ *         that need to be load balanced, for convenient iterative
+ *         access by the subsequent code that finds the best partition,
+ *         i.e the set of domains (subsets) of CPUs such that the
+ *         cpus_allowed of every cpuset marked is_sched_load_balance
+ *         is a subset of one of these domains, while there are as
+ *         many such domains as possible, each as small as possible.
+ * doms  - Conversion of 'csa' to an array of cpumasks, for passing to
+ *         the kernel/sched.c routine partition_sched_domains() in a
+ *         convenient format, that can be easily compared to the prior
+ *         value to determine what partition elements (sched domains)
+ *         were changed (added or removed.)
+ *
+ * Finding the best partition (set of domains):
+ *      The triple nested loops below over i, j, k scan over the
+ *      load balanced cpusets (using the array of cpuset pointers in
+ *      csa[]) looking for pairs of cpusets that have overlapping
+ *      cpus_allowed, but which don't have the same 'pn' partition
+ *      number and gives them in the same partition number.  It keeps
+ *      looping on the 'restart' label until it can no longer find
+ *      any such pairs.
+ *
+ *      The union of the cpus_allowed masks from the set of
+ *      all cpusets having the same 'pn' value then form the one
+ *      element of the partition (one sched domain) to be passed to
+ *      partition_sched_domains().
+ */
+
+static void rebuild_sched_domains(void)
+{
+        struct kfifo *q;        /* queue of cpusets to be scanned */
+        struct cpuset *cp;      /* scans q */
+        struct cpuset **csa;    /* array of all cpuset ptrs */
+        int csn;                /* how many cpuset ptrs in csa so far */
+        int i, j, k;            /* indices for partition finding loops */
+        cpumask_t *doms;        /* resulting partition; i.e. sched domains */
+        int ndoms;              /* number of sched domains in result */
+        int nslot;              /* next empty doms[] cpumask_t slot */
+
+        q = NULL;
+        csa = NULL;
+        doms = NULL;
+
+        /* Special case for the 99% of systems with one, full, sched domain */
+        if (is_sched_load_balance(&top_cpuset)) {
+                ndoms = 1;
+                doms = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
+                if (!doms)
+                        goto rebuild;
+                *doms = top_cpuset.cpus_allowed;
+                goto rebuild;
+        }
+
+        q = kfifo_alloc(number_of_cpusets * sizeof(cp), GFP_KERNEL, NULL);
+        if (IS_ERR(q))
+                goto done;
+        csa = kmalloc(number_of_cpusets * sizeof(cp), GFP_KERNEL);
+        if (!csa)
+                goto done;
+        csn = 0;
+
+        cp = &top_cpuset;
+        __kfifo_put(q, (void *)&cp, sizeof(cp));
+        while (__kfifo_get(q, (void *)&cp, sizeof(cp))) {
+                struct cgroup *cont;
+                struct cpuset *child;   /* scans child cpusets of cp */
+                if (is_sched_load_balance(cp))
+                        csa[csn++] = cp;
+                list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
+                        child = cgroup_cs(cont);
+                        __kfifo_put(q, (void *)&child, sizeof(cp));
+                }
+        }
+
+        for (i = 0; i < csn; i++)
+                csa[i]->pn = i;
+        ndoms = csn;
+
+restart:
+        /* Find the best partition (set of sched domains) */
+        for (i = 0; i < csn; i++) {
+                struct cpuset *a = csa[i];
+                int apn = a->pn;
+
+                for (j = 0; j < csn; j++) {
+                        struct cpuset *b = csa[j];
+                        int bpn = b->pn;
+
+                        if (apn != bpn && cpusets_overlap(a, b)) {
+                                for (k = 0; k < csn; k++) {
+                                        struct cpuset *c = csa[k];
+
+                                        if (c->pn == bpn)
+                                                c->pn = apn;
+                                }
+                                ndoms--;        /* one less element */
+                                goto restart;
+                        }
+                }
+        }
+
+        /* Convert <csn, csa> to <ndoms, doms> */
+        doms = kmalloc(ndoms * sizeof(cpumask_t), GFP_KERNEL);
+        if (!doms)
+                goto rebuild;
+
+        for (nslot = 0, i = 0; i < csn; i++) {
+                struct cpuset *a = csa[i];
+                int apn = a->pn;
+
+                if (apn >= 0) {
+                        cpumask_t *dp = doms + nslot;
+
+                        if (nslot == ndoms) {
+                                static int warnings = 10;
+                                if (warnings) {
+                                        printk(KERN_WARNING
+                                         "rebuild_sched_domains confused:"
+                                          " nslot %d, ndoms %d, csn %d, i %d,"
+                                          " apn %d\n",
+                                          nslot, ndoms, csn, i, apn);
+                                        warnings--;
+                                }
+                                continue;
+                        }
+
+                        cpus_clear(*dp);
+                        for (j = i; j < csn; j++) {
+                                struct cpuset *b = csa[j];
+
+                                if (apn == b->pn) {
+                                        cpus_or(*dp, *dp, b->cpus_allowed);
+                                        b->pn = -1;
+                                }
+                        }
+                        nslot++;
+                }
+        }
+        BUG_ON(nslot != ndoms);
+
+rebuild:
+        /* Have scheduler rebuild sched domains */
+        lock_cpu_hotplug();
+        partition_sched_domains(ndoms, doms);
+        unlock_cpu_hotplug();
+
+done:
+        if (q && !IS_ERR(q))
+                kfifo_free(q);
+        kfree(csa);
+        /* Don't kfree(doms) -- partition_sched_domains() does that. */
+}
+
+/*
  * Call with manage_mutex held.  May take callback_mutex during call.
  */
 
@@ -489,6 +701,7 @@ static int update_cpumask(struct cpuset *cs, char *buf)
 {
         struct cpuset trialcs;
         int retval;
+        int cpus_changed, is_load_balanced;
 
         /* top_cpuset.cpus_allowed tracks cpu_online_map; it's read-only */
         if (cs == &top_cpuset)
@@ -516,9 +729,17 @@ static int update_cpumask(struct cpuset *cs, char *buf)
         retval = validate_change(cs, &trialcs);
         if (retval < 0)
                 return retval;
+
+        cpus_changed = !cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed);
+        is_load_balanced = is_sched_load_balance(&trialcs);
+
         mutex_lock(&callback_mutex);
         cs->cpus_allowed = trialcs.cpus_allowed;
         mutex_unlock(&callback_mutex);
+
+        if (cpus_changed && is_load_balanced)
+                rebuild_sched_domains();
+
         return 0;
 }
 
@@ -752,6 +973,7 @@ static int update_memory_pressure_enabled(struct cpuset *cs, char *buf)
 /*
  * update_flag - read a 0 or a 1 in a file and update associated flag
  * bit: the bit to update (CS_CPU_EXCLUSIVE, CS_MEM_EXCLUSIVE,
+ *                              CS_SCHED_LOAD_BALANCE,
  *                              CS_NOTIFY_ON_RELEASE, CS_MEMORY_MIGRATE,
  *                              CS_SPREAD_PAGE, CS_SPREAD_SLAB)
  * cs:  the cpuset to update
@@ -765,6 +987,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
         int turning_on;
         struct cpuset trialcs;
         int err;
+        int cpus_nonempty, balance_flag_changed;
 
         turning_on = (simple_strtoul(buf, NULL, 10) != 0);
 
@@ -777,10 +1000,18 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
         err = validate_change(cs, &trialcs);
         if (err < 0)
                 return err;
+
+        cpus_nonempty = !cpus_empty(trialcs.cpus_allowed);
+        balance_flag_changed = (is_sched_load_balance(cs) !=
+                                        is_sched_load_balance(&trialcs));
+
         mutex_lock(&callback_mutex);
         cs->flags = trialcs.flags;
         mutex_unlock(&callback_mutex);
 
+        if (cpus_nonempty && balance_flag_changed)
+                rebuild_sched_domains();
+
         return 0;
 }
 
@@ -928,6 +1159,7 @@ typedef enum {
         FILE_MEMLIST,
         FILE_CPU_EXCLUSIVE,
         FILE_MEM_EXCLUSIVE,
+        FILE_SCHED_LOAD_BALANCE,
         FILE_MEMORY_PRESSURE_ENABLED,
         FILE_MEMORY_PRESSURE,
         FILE_SPREAD_PAGE,
@@ -946,7 +1178,7 @@ static ssize_t cpuset_common_file_write(struct cgroup *cont,
         int retval = 0;
 
         /* Crude upper limit on largest legitimate cpulist user might write. */
-        if (nbytes > 100 + 6 * max(NR_CPUS, MAX_NUMNODES))
+        if (nbytes > 100U + 6 * max(NR_CPUS, MAX_NUMNODES))
                 return -E2BIG;
 
         /* +1 for nul-terminator */
@@ -979,6 +1211,9 @@ static ssize_t cpuset_common_file_write(struct cgroup *cont,
         case FILE_MEM_EXCLUSIVE:
                 retval = update_flag(CS_MEM_EXCLUSIVE, cs, buffer);
                 break;
+        case FILE_SCHED_LOAD_BALANCE:
+                retval = update_flag(CS_SCHED_LOAD_BALANCE, cs, buffer);
+                break;
         case FILE_MEMORY_MIGRATE:
                 retval = update_flag(CS_MEMORY_MIGRATE, cs, buffer);
                 break;
@@ -1074,6 +1309,9 @@ static ssize_t cpuset_common_file_read(struct cgroup *cont,
         case FILE_MEM_EXCLUSIVE:
                 *s++ = is_mem_exclusive(cs) ? '1' : '0';
                 break;
+        case FILE_SCHED_LOAD_BALANCE:
+                *s++ = is_sched_load_balance(cs) ? '1' : '0';
+                break;
         case FILE_MEMORY_MIGRATE:
                 *s++ = is_memory_migrate(cs) ? '1' : '0';
                 break;
@@ -1137,6 +1375,13 @@ static struct cftype cft_mem_exclusive = {
         .private = FILE_MEM_EXCLUSIVE,
 };
 
+static struct cftype cft_sched_load_balance = {
+        .name = "sched_load_balance",
+        .read = cpuset_common_file_read,
+        .write = cpuset_common_file_write,
+        .private = FILE_SCHED_LOAD_BALANCE,
+};
+
 static struct cftype cft_memory_migrate = {
         .name = "memory_migrate",
         .read = cpuset_common_file_read,
@@ -1186,6 +1431,8 @@ static int cpuset_populate(struct cgroup_subsys *ss, struct cgroup *cont)
                 return err;
         if ((err = cgroup_add_file(cont, ss, &cft_memory_migrate)) < 0)
                 return err;
+        if ((err = cgroup_add_file(cont, ss, &cft_sched_load_balance)) < 0)
+                return err;
         if ((err = cgroup_add_file(cont, ss, &cft_memory_pressure)) < 0)
                 return err;
         if ((err = cgroup_add_file(cont, ss, &cft_spread_page)) < 0)
@@ -1267,6 +1514,7 @@ static struct cgroup_subsys_state *cpuset_create(
                 set_bit(CS_SPREAD_PAGE, &cs->flags);
         if (is_spread_slab(parent))
                 set_bit(CS_SPREAD_SLAB, &cs->flags);
+        set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
         cs->cpus_allowed = CPU_MASK_NONE;
         cs->mems_allowed = NODE_MASK_NONE;
         cs->mems_generation = cpuset_mems_generation++;
@@ -1277,11 +1525,27 @@ static struct cgroup_subsys_state *cpuset_create(
         return &cs->css ;
 }
 
+/*
+ * Locking note on the strange update_flag() call below:
+ *
+ * If the cpuset being removed has its flag 'sched_load_balance'
+ * enabled, then simulate turning sched_load_balance off, which
+ * will call rebuild_sched_domains().  The lock_cpu_hotplug()
+ * call in rebuild_sched_domains() must not be made while holding
+ * callback_mutex.  Elsewhere the kernel nests callback_mutex inside
+ * lock_cpu_hotplug() calls.  So the reverse nesting would risk an
+ * ABBA deadlock.
+ */
+
 static void cpuset_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
 {
         struct cpuset *cs = cgroup_cs(cont);
 
         cpuset_update_task_memory_state();
+
+        if (is_sched_load_balance(cs))
+                update_flag(CS_SCHED_LOAD_BALANCE, cs, "0");
+
         number_of_cpusets--;
         kfree(cs);
 }
@@ -1326,6 +1590,7 @@ int __init cpuset_init(void)
 
         fmeter_init(&top_cpuset.fmeter);
         top_cpuset.mems_generation = cpuset_mems_generation++;
+        set_bit(CS_SCHED_LOAD_BALANCE, &top_cpuset.flags);
 
         err = register_filesystem(&cpuset_fs_type);
         if (err < 0)
@@ -1412,8 +1677,8 @@ static void common_cpu_mem_hotplug_unplug(void)
  * cpu_online_map on each CPU hotplug (cpuhp) event.
  */
 
-static int cpuset_handle_cpuhp(struct notifier_block *nb,
-                                unsigned long phase, void *cpu)
+static int cpuset_handle_cpuhp(struct notifier_block *unused_nb,
+                                unsigned long phase, void *unused_cpu)
 {
         if (phase == CPU_DYING || phase == CPU_DYING_FROZEN)
                 return NOTIFY_DONE;
@@ -1803,7 +2068,7 @@ void __cpuset_memory_pressure_bump(void)
  *    the_top_cpuset_hack in cpuset_exit(), which sets an exiting tasks
  *    cpuset to top_cpuset.
  */
-static int proc_cpuset_show(struct seq_file *m, void *v)
+static int proc_cpuset_show(struct seq_file *m, void *unused_v)
 {
         struct pid *pid;
         struct task_struct *tsk;
diff --git a/kernel/sched.c b/kernel/sched.c
index 5d5e107ebc4e..39d6354af489 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6376,26 +6376,31 @@ error:
         return -ENOMEM;
 #endif
 }
+
+static cpumask_t *doms_cur;     /* current sched domains */
+static int ndoms_cur;           /* number of sched domains in 'doms_cur' */
+
+/*
+ * Special case: If a kmalloc of a doms_cur partition (array of
+ * cpumask_t) fails, then fallback to a single sched domain,
+ * as determined by the single cpumask_t fallback_doms.
+ */
+static cpumask_t fallback_doms;
+
 /*
  * Set up scheduler domains and groups.  Callers must hold the hotplug lock.
+ * For now this just excludes isolated cpus, but could be used to
+ * exclude other special cases in the future.
  */
 static int arch_init_sched_domains(const cpumask_t *cpu_map)
 {
-        cpumask_t cpu_default_map;
-        int err;
-
-        /*
-         * Setup mask for cpus without special case scheduling requirements.
-         * For now this just excludes isolated cpus, but could be used to
-         * exclude other special cases in the future.
-         */
-        cpus_andnot(cpu_default_map, *cpu_map, cpu_isolated_map);
-
-        err = build_sched_domains(&cpu_default_map);
-
+        ndoms_cur = 1;
+        doms_cur = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
+        if (!doms_cur)
+                doms_cur = &fallback_doms;
+        cpus_andnot(*doms_cur, *cpu_map, cpu_isolated_map);
         register_sched_domain_sysctl();
-
-        return err;
+        return build_sched_domains(doms_cur);
 }
 
 static void arch_destroy_sched_domains(const cpumask_t *cpu_map)
@@ -6419,6 +6424,68 @@ static void detach_destroy_domains(const cpumask_t *cpu_map)
         arch_destroy_sched_domains(cpu_map);
 }
 
+/*
+ * Partition sched domains as specified by the 'ndoms_new'
+ * cpumasks in the array doms_new[] of cpumasks.  This compares
+ * doms_new[] to the current sched domain partitioning, doms_cur[].
+ * It destroys each deleted domain and builds each new domain.
+ *
+ * 'doms_new' is an array of cpumask_t's of length 'ndoms_new'.
+ * The masks don't intersect (don't overlap.)  We should setup one
+ * sched domain for each mask.  CPUs not in any of the cpumasks will
+ * not be load balanced.  If the same cpumask appears both in the
+ * current 'doms_cur' domains and in the new 'doms_new', we can leave
+ * it as it is.
+ *
+ * The passed in 'doms_new' should be kmalloc'd.  This routine takes
+ * ownership of it and will kfree it when done with it.  If the caller
+ * failed the kmalloc call, then it can pass in doms_new == NULL,
+ * and partition_sched_domains() will fallback to the single partition
+ * 'fallback_doms'.
+ *
+ * Call with hotplug lock held
+ */
+void partition_sched_domains(int ndoms_new, cpumask_t *doms_new)
+{
+        int i, j;
+
+        if (doms_new == NULL) {
+                ndoms_new = 1;
+                doms_new = &fallback_doms;
+                cpus_andnot(doms_new[0], cpu_online_map, cpu_isolated_map);
+        }
+
+        /* Destroy deleted domains */
+        for (i = 0; i < ndoms_cur; i++) {
+                for (j = 0; j < ndoms_new; j++) {
+                        if (cpus_equal(doms_cur[i], doms_new[j]))
+                                goto match1;
+                }
+                /* no match - a current sched domain not in new doms_new[] */
+                detach_destroy_domains(doms_cur + i);
+match1:
+                ;
+        }
+
+        /* Build new domains */
+        for (i = 0; i < ndoms_new; i++) {
+                for (j = 0; j < ndoms_cur; j++) {
+                        if (cpus_equal(doms_new[i], doms_cur[j]))
+                                goto match2;
+                }
+                /* no match - add a new doms_new */
+                build_sched_domains(doms_new + i);
+match2:
+                ;
+        }
+
+        /* Remember the new sched domains */
+        if (doms_cur != &fallback_doms)
+                kfree(doms_cur);
+        doms_cur = doms_new;
+        ndoms_cur = ndoms_new;
+}
+
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
 static int arch_reinit_sched_domains(void)
 {