| Message ID | 1423012341-30265-2-git-send-email-xlpang@126.com |
|---|---|
| State | New |
| Headers | show |
Hi Steve, On 4 February 2015 at 11:17, Steven Rostedt <rostedt@goodmis.org> wrote: > On Wed, 4 Feb 2015 09:12:21 +0800 > Xunlei Pang <xlpang@126.com> wrote: > >> From: Xunlei Pang <pang.xunlei@linaro.org> >> >> check_preempt_curr() doesn't call sched_class::check_preempt_curr >> when the class of current is a higher level. So if there is a DL >> task running when doing this for RT, check_preempt_equal_prio() >> will definitely miss, which may result in some response latency >> for this RT task if it is pinned and there're some same-priority >> migratable rt tasks already queued. >> >> We should do the similar thing in select_task_rq_rt() when first >> picking rt tasks after running out of DL tasks. >> >> This patch tackles the issue by peeking the next rt task(RT1), and >> if find RT1 migratable, just requeue it to the tail of the rq using >> requeue_task_rt(rq, p, 0). In this way: >> - If there do have another rt task(RT2) with the same priority as >> RT1, RT2 will finally be picked as the running task. While RT1 >> will be pushed onto another cpu via RT1's post_schedule(), as >> RT1 is migratable. The difference from check_preempt_equal_prio() >> here is that we just don't care whether RT2 is migratable. >> >> - Otherwise, if there's no rt task with the same priority as RT1, >> RT1 will still be picked as the running task after the requeuing. >> >> Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org> >> --- >> kernel/sched/rt.c | 15 +++++++++++++++ >> 1 file changed, 15 insertions(+) >> >> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c >> index 4dacb6e..b2385ee 100644 >> --- a/kernel/sched/rt.c >> +++ b/kernel/sched/rt.c >> @@ -1477,6 +1477,21 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev) >> >> put_prev_task(rq, prev); >> >> +#ifdef CONFIG_SMP >> + /* >> + * If there's a running deadline task, check_preempt_curr() >> + * doesn't invoke check_preempt_curr_rt() for rt tasks, so >> + * we can do it here. >> + */ > > Why the strange indentation? > Thanks for catching this, I'll fix it. >> + if (prev->sched_class == &dl_sched_class && >> + rq->rt.rt_nr_total > 1) { >> + p = _pick_next_task_rt(rq, 1); /* peek only */ > > I hate the "peek only". Just split the function into two, where you > have something like check_next_task(rq) which does your "peek only" > and the __pick_next_task_rt() calls check_next_task() first and then > runs the rest of the code. > This sounds good, I'll make a new peek_next_task_rt() as the base one. Thanks, Xunlei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 4dacb6e..b2385ee 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1477,6 +1477,21 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev) put_prev_task(rq, prev); +#ifdef CONFIG_SMP + /* + * If there's a running deadline task, check_preempt_curr() + * doesn't invoke check_preempt_curr_rt() for rt tasks, so + * we can do it here. + */ + if (prev->sched_class == &dl_sched_class && + rq->rt.rt_nr_total > 1) { + p = _pick_next_task_rt(rq, 1); /* peek only */ + if (p->nr_cpus_allowed != 1 && + cpupri_find(&rq->rd->cpupri, p, NULL)) + requeue_task_rt(rq, p, 0); + } +#endif + p = _pick_next_task_rt(rq, 0); /* The running task is never eligible for pushing */