diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2014-02-14 15:25:08 +0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2014-02-27 15:41:02 +0400 |
| commit | 37e117c07b89194aae7062bc63bde1104c03db02 (patch) | |
| tree | 770312bf789e367b8f2102e9f8de743f05efeeac /kernel/sched/fair.c | |
| parent | 06d50c65b1043b166d102accc081093f79d8f7e5 (diff) | |
| download | linux-37e117c07b89194aae7062bc63bde1104c03db02.tar.xz | |
sched: Guarantee task priority in pick_next_task()
Michael spotted that the idle_balance() push down created a task
priority problem.
Previously, when we called idle_balance() before pick_next_task() it
wasn't a problem when -- because of the rq->lock droppage -- an rt/dl
task slipped in.
Similarly for pre_schedule(), rt pre-schedule could have a dl task
slip in.
But by pulling it into the pick_next_task() loop, we'll not try a
higher task priority again.
Cure this by creating a re-start condition in pick_next_task(); and
triggering this from pick_next_task_{rt,fair}().
It also fixes a live-lock where we get stuck in pick_next_task_fair()
due to idle_balance() seeing !0 nr_running but there not actually
being any fair tasks about.
Reported-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Fixes: 38033c37faab ("sched: Push down pre_schedule() and idle_balance()")
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20140224121218.GR15586@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/fair.c')
| -rw-r--r-- | kernel/sched/fair.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index be4f7d9eaf03..16042b58a32f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4686,6 +4686,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev) struct cfs_rq *cfs_rq = &rq->cfs; struct sched_entity *se; struct task_struct *p; + int new_tasks; again: #ifdef CONFIG_FAIR_GROUP_SCHED @@ -4784,7 +4785,17 @@ simple: return p; idle: - if (idle_balance(rq)) /* drops rq->lock */ + /* + * Because idle_balance() releases (and re-acquires) rq->lock, it is + * possible for any higher priority task to appear. In that case we + * must re-start the pick_next_entity() loop. + */ + new_tasks = idle_balance(rq); + + if (rq->nr_running != rq->cfs.h_nr_running) + return RETRY_TASK; + + if (new_tasks) goto again; return NULL; |