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authorNick Piggin <nickpiggin@yahoo.com.au>2005-09-10 00:26:18 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-10 10:06:23 -0700
commite17224bf1d01b461ec02a60f5a9b7657a89bdd23 (patch)
tree30dbb20798fde88a09680e9d82bd32ad8c343692 /kernel
parentd6d5cfaf4551aa7713ca6ab73bb77e832602204b (diff)
[PATCH] sched: less locking
During periodic load balancing, don't hold this runqueue's lock while scanning remote runqueues, which can take a non trivial amount of time especially on very large systems. Holding the runqueue lock will only help to stabilise ->nr_running, however this doesn't do much to help because tasks being woken will simply get held up on the runqueue lock, so ->nr_running would not provide a really accurate picture of runqueue load in that case anyway. What's more, ->nr_running (and possibly the cpu_load averages) of remote runqueues won't be stable anyway, so load balancing is always an inexact operation. Signed-off-by: Nick Piggin <npiggin@suse.de> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c9
1 files changed, 2 insertions, 7 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 930189540f3b..8535e5c68f5b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2075,7 +2075,6 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
int nr_moved, all_pinned = 0;
int active_balance = 0;
- spin_lock(&this_rq->lock);
schedstat_inc(sd, lb_cnt[idle]);
group = find_busiest_group(sd, this_cpu, &imbalance, idle);
@@ -2102,18 +2101,16 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
* still unbalanced. nr_moved simply stays zero, so it is
* correctly treated as an imbalance.
*/
- double_lock_balance(this_rq, busiest);
+ double_rq_lock(this_rq, busiest);
nr_moved = move_tasks(this_rq, this_cpu, busiest,
imbalance, sd, idle, &all_pinned);
- spin_unlock(&busiest->lock);
+ double_rq_unlock(this_rq, busiest);
/* All tasks on this runqueue were pinned by CPU affinity */
if (unlikely(all_pinned))
goto out_balanced;
}
- spin_unlock(&this_rq->lock);
-
if (!nr_moved) {
schedstat_inc(sd, lb_failed[idle]);
sd->nr_balance_failed++;
@@ -2156,8 +2153,6 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
return nr_moved;
out_balanced:
- spin_unlock(&this_rq->lock);
-
schedstat_inc(sd, lb_balanced[idle]);
sd->nr_balance_failed = 0;

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