4.2-stable review patch. If anyone has any objections, please let me know.
------------------ From: Luca Abeni <[email protected]> commit 5aa5050787f449e7eaef2c5ec93c7b357aa7dcdc upstream. Commit: 9d5142624256 ("sched/deadline: Reduce rq lock contention by eliminating locking of non-feasible target") broke select_task_rq_dl() and find_lock_later_rq(), because it introduced a comparison between the local task's deadline and dl.earliest_dl.curr of the remote queue. However, if the remote runqueue does not contain any SCHED_DEADLINE task its earliest_dl.curr is 0 (always smaller than the deadline of the local task) and the remote runqueue is not selected for pushing. As a result, if an application creates multiple SCHED_DEADLINE threads, they will never be pushed to runqueues that do not already contain SCHED_DEADLINE tasks. This patch fixes the issue by checking if dl.dl_nr_running == 0. Signed-off-by: Luca Abeni <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Juri Lelli <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Wanpeng Li <[email protected]> Fixes: 9d5142624256 ("sched/deadline: Reduce rq lock contention by eliminating locking of non-feasible target") Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/sched/deadline.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1066,8 +1066,9 @@ select_task_rq_dl(struct task_struct *p, int target = find_later_rq(p); if (target != -1 && - dl_time_before(p->dl.deadline, - cpu_rq(target)->dl.earliest_dl.curr)) + (dl_time_before(p->dl.deadline, + cpu_rq(target)->dl.earliest_dl.curr) || + (cpu_rq(target)->dl.dl_nr_running == 0))) cpu = target; } rcu_read_unlock(); @@ -1417,7 +1418,8 @@ static struct rq *find_lock_later_rq(str later_rq = cpu_rq(cpu); - if (!dl_time_before(task->dl.deadline, + if (later_rq->dl.dl_nr_running && + !dl_time_before(task->dl.deadline, later_rq->dl.earliest_dl.curr)) { /* * Target rq has tasks of equal or earlier deadline, -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
