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author | Peter Zijlstra <peterz@infradead.org> | 2014-02-14 12:25:08 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2014-02-27 12:41:02 +0100 |
commit | 37e117c07b89194aae7062bc63bde1104c03db02 (patch) | |
tree | 770312bf789e367b8f2102e9f8de743f05efeeac /kernel/sched/sched.h | |
parent | sched/idle: Remove stale old file (diff) | |
download | linux-37e117c07b89194aae7062bc63bde1104c03db02.tar.xz linux-37e117c07b89194aae7062bc63bde1104c03db02.zip |
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/sched.h')
-rw-r--r-- | kernel/sched/sched.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 046084ebb1fb..1929deb3f29d 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1091,6 +1091,8 @@ static const u32 prio_to_wmult[40] = { #define DEQUEUE_SLEEP 1 +#define RETRY_TASK ((void *)-1UL) + struct sched_class { const struct sched_class *next; @@ -1105,6 +1107,9 @@ struct sched_class { * It is the responsibility of the pick_next_task() method that will * return the next task to call put_prev_task() on the @prev task or * something equivalent. + * + * May return RETRY_TASK when it finds a higher prio class has runnable + * tasks. */ struct task_struct * (*pick_next_task) (struct rq *rq, struct task_struct *prev); |