sched: pull only one task during NEWIDLE balancing to limit critical section (7e96fa58) · Commits · 戴 / test

git-id attempted to limit newidle critical section length by stopping after at least one task was moved. Further investigation has shown that there are other paths nested further inside the algorithm which still remain that allow long latencies to occur with newidle balancing. This patch applies the same technique inside balance_tasks() to limit the duration of this optional balancing operation. Signed-off-by:

Gregory Haskins <ghaskins@novell.com> CC: Nick Piggin <npiggin@suse.de>

kernel/sched.c

+17 −1

Original line number	Diff line number	Diff line
		@@ -2984,6 +2984,16 @@ next:
		pulled++;
		rem_load_move -= p->se.load.weight;

		#ifdef CONFIG_PREEMPT
		/*
		* NEWIDLE balancing is a source of latency, so preemptible kernels
		* will stop after the first task is pulled to minimize the critical
		* section.
		*/
		if (idle == CPU_NEWLY_IDLE)
		goto out;
		#endif

		/*
		* We only want to steal up to the prescribed amount of weighted load.
		*/
		@@ -3030,9 +3040,15 @@ static int move_tasks(struct rq this_rq, int this_cpu, struct rq busiest,
		sd, idle, all_pinned, &this_best_prio);
		class = class->next;

		#ifdef CONFIG_PREEMPT
		/*
		* NEWIDLE balancing is a source of latency, so preemptible
		* kernels will stop after the first task is pulled to minimize
		* the critical section.
		*/
		if (idle == CPU_NEWLY_IDLE && this_rq->nr_running)
		break;

		#endif
		} while (class && max_load_move > total_load_moved);

		return total_load_moved > 0;

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