Messages in this thread | | | Date | Mon, 20 Apr 2015 10:52:28 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v6 2/3] sched/rt: Fix wrong SMP scheduler behavior for equal prio cases |
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On Mon, 20 Apr 2015 16:22:47 +0800 Xunlei Pang <xlpang@126.com> wrote:
> static inline void enqueue_pushable_task(struct rq *rq, struct task_struct *p) > { > } > @@ -1506,8 +1526,21 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p) > * The previous task needs to be made eligible for pushing > * if it is still active > */ > - if (on_rt_rq(&p->rt) && p->nr_cpus_allowed > 1) > - enqueue_pushable_task(rq, p); > + if (on_rt_rq(&p->rt) && p->nr_cpus_allowed > 1) { > + /* > + * put_prev_task_rt() is called by many functions, > + * pick_next_task_rt() is the only one may have > + * PREEMPT_ACTIVE set. So if detecting p(current > + * task) is preempted in such case, we should > + * enqueue it to the front of the pushable plist, > + * as there may be multiple tasks with the same > + * priority as p.
The above comment is very difficult to understand. Maybe something like:
/* * When put_prev_task_rt() is called by * pick_next_task_rt(), if PREEMPT_ACTIVE is set, it * means that the current rt task is being preempted by * a higher priority task. To maintain FIFO, it must * stay ahead of any other task that is queued at the * same priority. */
-- Steve
> + */ > + if (preempt_count() & PREEMPT_ACTIVE) > + enqueue_pushable_task_preempted(rq, p); > + else > + enqueue_pushable_task(rq, p); > + } > } > > #ifdef CONFIG_SMP
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