sched: avoid large irq-latencies in smp-balancing

[net-next-2.6.git] / kernel / sched.c

diff --git a/kernel/sched.c b/kernel/sched.c
index 2a107e4ad5eda381358d78f318562bcf472c848c..e195a422941802b8660a2d59922b08026a030b12 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -471,6 +471,12 @@ const_debug unsigned int sysctl_sched_features =
 
 #define sched_feat(x) (sysctl_sched_features & SCHED_FEAT_##x)
 
+/*
+ * Number of tasks to iterate in a single balance run.
+ * Limited because this is done with IRQs disabled.
+ */
+const_debug unsigned int sysctl_sched_nr_migrate = 32;
+
 /*
  * For kernel-internal use: high-speed (but slightly incorrect) per-cpu
  * clock constructed from sched_clock():
@@ -2235,7 +2241,7 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
              enum cpu_idle_type idle, int *all_pinned,
              int *this_best_prio, struct rq_iterator *iterator)
 {
-       int pulled = 0, pinned = 0, skip_for_load;
+       int loops = 0, pulled = 0, pinned = 0, skip_for_load;
        struct task_struct *p;
        long rem_load_move = max_load_move;
 
@@ -2249,10 +2255,10 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
         */
        p = iterator->start(iterator->arg);
 next:
-       if (!p)
+       if (!p || loops++ > sysctl_sched_nr_migrate)
                goto out;
        /*
-        * To help distribute high priority tasks accross CPUs we don't
+        * To help distribute high priority tasks across CPUs we don't
         * skip a task if it will be the highest priority task (i.e. smallest
         * prio value) on its new queue regardless of its load weight
         */
@@ -2269,8 +2275,7 @@ next:
        rem_load_move -= p->se.load.weight;
 
        /*
-        * We only want to steal up to the prescribed number of tasks
-        * and the prescribed amount of weighted load.
+        * We only want to steal up to the prescribed amount of weighted load.
         */
        if (rem_load_move > 0) {
                if (p->prio < *this_best_prio)