[TIP/SCHED/DEVEL PATCH v3 2/6] sched: pull only one task during NEWIDLE balancing to limit critical section
From: Gregory Haskins <hidden>
Date: 2008-09-04 12:58:30
Also in:
lkml
Subsystem:
the rest · Maintainer:
Linus Torvalds
git-id c4acb2c0669c5c5c9b28e9d02a34b5c67edf7092 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 <redacted> CC: Nick Piggin <redacted> --- kernel/sched.c | 18 +++++++++++++++++- 1 files changed, 17 insertions(+), 1 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index b112caa..35e1f21 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c@@ -2962,6 +2962,16 @@ 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. */
@@ -3008,9 +3018,15 @@ 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;