Messages in this thread Patch in this message | | | From | Julien Desfossez <> | Subject | [RFC PATCH 1/6] sched/fair: check_preempt_wakeup: Fix assumption on the default policy | Date | Fri, 16 Sep 2016 17:09:03 -0400 |
| |
Tasks with RT or deadline scheduling class may inherit from a task with a "fair" scheduling class. This priority inheritance changes the scheduling class, but not the task "policy" field.
Therefore, the fair scheduler should not assume that policy != SCHED_NORMAL is the same as (policy == SCHED_BATCH || policy == SCHED_IDLE), because the policy could also be SCHED_RR, SCHED_FIFO, or SCHED_DEADLINE.
The incorrect comparison in check_preempt_wakeup makes RR, FIFO and DEADLINE tasks which inherit from a fair task behave as if they were IDLE or BATCH tasks, thus awaiting the following tick before preempting the current task.
Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt (Red Hat) <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Julien Desfossez <jdesfossez@efficios.com> --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 07aaa7f..f3aef21 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5669,7 +5669,8 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ * Batch and idle tasks do not preempt non-idle tasks (their preemption * is driven by the tick): */ - if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION)) + if (unlikely(p->policy == SCHED_BATCH || p->policy == SCHED_IDLE) || + !sched_feat(WAKEUP_PREEMPTION)) return; find_matching_se(&se, &pse); -- 1.9.1
| |