From: Nick Piggin <nickpiggin@yahoo.com.au>
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 <npiggin@suse.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
kernel/sched.c | 17 ++++++++++-------
1 files changed, 10 insertions(+), 7 deletions(-)
diff -puN kernel/sched.c~sched-less-newidle-locking kernel/sched.c
--- devel/kernel/sched.c~sched-less-newidle-locking 2005-09-07 20:11:03.000000000 -0700
+++ devel-akpm/kernel/sched.c 2005-09-07 20:11:03.000000000 -0700
@@ -2181,8 +2181,7 @@ 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 */
@@ -2277,18 +2276,22 @@ 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:
_