[PATCH] sched: reduce active load balancing

Fix up active load balancing a bit so it doesn't get called when it shouldn't.
Reset the nr_balance_failed counter at more points where we have found
conditions to be balanced.  This reduces too aggressive active balancing seen
on some workloads.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/sched.c b/kernel/sched.c
index 2794c79b91977c0980d849b73905e1e644296937..03d737791c1ad4f188b68dcd6a467c7bb21bab31 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2021,6 +2021,7 @@ out_balanced:
 
        schedstat_inc(sd, lb_balanced[idle]);
 
+       sd->nr_balance_failed = 0;
        /* tune up the balancing interval */
        if (sd->balance_interval < sd->max_interval)
                sd->balance_interval *= 2;
@@ -2046,16 +2047,14 @@ static int load_balance_newidle(int this_cpu, runqueue_t *this_rq,
        schedstat_inc(sd, lb_cnt[NEWLY_IDLE]);
        group = find_busiest_group(sd, this_cpu, &imbalance, NEWLY_IDLE);
        if (!group) {
-               schedstat_inc(sd, lb_balanced[NEWLY_IDLE]);
                schedstat_inc(sd, lb_nobusyg[NEWLY_IDLE]);
-               goto out;
+               goto out_balanced;
        }
 
        busiest = find_busiest_queue(group);
        if (!busiest || busiest == this_rq) {
-               schedstat_inc(sd, lb_balanced[NEWLY_IDLE]);
                schedstat_inc(sd, lb_nobusyq[NEWLY_IDLE]);
-               goto out;
+               goto out_balanced;
        }
 
        /* Attempt to move tasks */
@@ -2066,11 +2065,16 @@ static int load_balance_newidle(int this_cpu, runqueue_t *this_rq,
                                        imbalance, sd, NEWLY_IDLE, NULL);
        if (!nr_moved)
                schedstat_inc(sd, lb_failed[NEWLY_IDLE]);
+       else
+               sd->nr_balance_failed = 0;
 
        spin_unlock(&busiest->lock);
-
-out:
        return nr_moved;
+
+out_balanced:
+       schedstat_inc(sd, lb_balanced[NEWLY_IDLE]);
+       sd->nr_balance_failed = 0;
+       return 0;
 }
 
 /*