+/*
+ * 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 get_online_cpus()/put_online_cpus() pair.
+ * Must not be called holding callback_mutex, because we must not
+ * call get_online_cpus() while holding callback_mutex. Elsewhere
+ * the kernel nests callback_mutex inside get_online_cpus() 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 */
+ get_online_cpus();
+ partition_sched_domains(ndoms, doms);
+ put_online_cpus();
+
+done:
+ if (q && !IS_ERR(q))
+ kfifo_free(q);
+ kfree(csa);
+ /* Don't kfree(doms) -- partition_sched_domains() does that. */
+}
+
+static inline int started_after_time(struct task_struct *t1,
+ struct timespec *time,
+ struct task_struct *t2)
+{
+ int start_diff = timespec_compare(&t1->start_time, time);
+ if (start_diff > 0) {
+ return 1;
+ } else if (start_diff < 0) {
+ return 0;
+ } else {
+ /*
+ * Arbitrarily, if two processes started at the same
+ * time, we'll say that the lower pointer value
+ * started first. Note that t2 may have exited by now
+ * so this may not be a valid pointer any longer, but
+ * that's fine - it still serves to distinguish
+ * between two tasks started (effectively)
+ * simultaneously.
+ */
+ return t1 > t2;
+ }
+}
+
+static inline int started_after(void *p1, void *p2)
+{
+ struct task_struct *t1 = p1;
+ struct task_struct *t2 = p2;
+ return started_after_time(t1, &t2->start_time, t2);
+}
+