From: Nick Piggin 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 --- kernel/sched.c | 9 ++------- 1 files changed, 2 insertions(+), 7 deletions(-) diff -puN kernel/sched.c~sched-less-locking kernel/sched.c --- devel/kernel/sched.c~sched-less-locking 2005-08-30 18:45:57.000000000 -0700 +++ devel-akpm/kernel/sched.c 2005-08-30 18:45:57.000000000 -0700 @@ -2146,7 +2146,6 @@ static int load_balance(int this_cpu, ru 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); @@ -2173,18 +2172,16 @@ static int load_balance(int this_cpu, ru * 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++; @@ -2227,8 +2224,6 @@ static int load_balance(int this_cpu, ru return nr_moved; out_balanced: - spin_unlock(&this_rq->lock); - schedstat_inc(sd, lb_balanced[idle]); sd->nr_balance_failed = 0; _