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SUSE Labs, Novell Inc.
Similarly to the earlier change in load_balance, only lock the runqueue
in load_balance_newidle if the busiest queue found has a nr_running > 1.
This will reduce frequency of expensive remote runqueue lock aquisitions
in the schedule() path on some workloads.
Signed-off-by: Nick Piggin <[email protected]>
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c 2005-08-02 21:35:36.000000000 +1000
+++ linux-2.6/kernel/sched.c 2005-08-02 21:56:40.000000000 +1000
@@ -2080,8 +2080,7 @@ static int load_balance(int this_cpu, ru
*/
double_lock_balance(this_rq, busiest);
nr_moved = move_tasks(this_rq, this_cpu, busiest,
- imbalance, sd, idle,
- &all_pinned);
+ imbalance, sd, idle, &all_pinned);
spin_unlock(&busiest->lock);
/* All tasks on this runqueue were pinned by CPU affinity */
@@ -2176,18 +2175,22 @@ static int load_balance_newidle(int this
BUG_ON(busiest == this_rq);
- /* Attempt to move tasks */
- double_lock_balance(this_rq, busiest);
-
schedstat_add(sd, lb_imbalance[NEWLY_IDLE], imbalance);
- nr_moved = move_tasks(this_rq, this_cpu, busiest,
+
+ nr_moved = 0;
+ if (busiest->nr_running > 1) {
+ /* Attempt to move tasks */
+ double_lock_balance(this_rq, busiest);
+ nr_moved = move_tasks(this_rq, this_cpu, busiest,
imbalance, sd, NEWLY_IDLE, NULL);
+ spin_unlock(&busiest->lock);
+ }
+
if (!nr_moved)
schedstat_inc(sd, lb_failed[NEWLY_IDLE]);
else
sd->nr_balance_failed = 0;
- spin_unlock(&busiest->lock);
return nr_moved;
out_balanced:
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