[PATCH] sched: less locking (e17224bf) · Commits · 戴 / test

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>

kernel/sched.c

+2 −7

Original line number	Diff line number	Diff line
		@@ -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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