From: Nick Piggin Date: Sat, 10 Sep 2005 07:26:18 +0000 (-0700) Subject: [PATCH] sched: less locking X-Git-Tag: v2.6.14-rc1~214 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e17224bf1d01b461ec02a60f5a9b7657a89bdd23;p=linux-2.6 [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 Acked-by: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/sched.c b/kernel/sched.c index 930189540f..8535e5c68f 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;