Messages in this thread | | | From | Kirill Tkhai <> | Subject | Re: [sched/rt] Optimization of function pull_rt_task() | Date | Tue, 18 Dec 2012 14:43:41 +0400 |
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16.11.2012, 00:36, "Steven Rostedt" <rostedt@goodmis.org>: > Doing my INBOX maintenance (clean up), I've stumbled on this thread > again. I'm not sure the changes here are hopeless. > > On Mon, 2012-06-04 at 13:27 +0800, Yong Zhang wrote: > >> On Fri, Jun 01, 2012 at 08:45:16PM +0400, Kirill Tkhai wrote: >>> 19.04.2012, 12:54, "Yong Zhang" <yong.zhang0@gmail.com>: >>>> On Wed, Apr 18, 2012 at 05:16:55PM -0400, Steven Rostedt wrote: >>>>> ?On Wed, 2012-04-18 at 14:32 -0400, Steven Rostedt wrote: >>>>>> ?On Mon, 2012-04-16 at 12:06 -0400, Steven Rostedt wrote: >>>>>>> ?On Sun, 2012-04-15 at 23:45 +0400, Kirill Tkhai wrote: >>>>>>>> ?The condition (src_rq->rt.rt_nr_running) is weak because it doesn't >>>>>>>> ?consider the cases when src_rq has only processes bound to it (when >>>>>>>> ?single cpu is allowed). It may be running kernel thread like >>>>>>>> ?migration/x etc. >>>>>>>> >>>>>>>> ?So it's better to use more stronger condition which is able to exclude >>>>>>>> ?above conditions. The function has_pushable_tasks() complitely does >>>>>>>> ?this. A task may be pullable for another cpu rq only if he is pushable >>>>>>>> ?for his own queue. >>>>>>> ?I considered this before, and for some reason I never did the change. >>>>>>> ?I'll have to think about it. It seems like this would be the obvious >>>>>>> ?case, but I think there was something not so obvious that caused issues. >>>>>>> ?But I don't remember what it was. >>>>>>> >>>>>>> ?I'll have to rethink this again. >>>>>> ?I can't find anything wrong with this change. Maybe things change, or I >>>>>> ?was thinking of another change. >>>>>> >>>>>> ?I'll apply it and start running my tests against it. >>>>> ?Not only does this seem to work fine, I took it one step further :-) >>>> Hmm... throttle doesn't handle the pushable list, so we may find a >>>> throttled task by pick_next_pushable_task(). >>>> >>>> Thanks, >>>> Yong >>> I don't complitelly understand throttle logic. >>> >>> Is the source patch not-appliable the same reason? >> I guess so. >> >> Your patch will change the semantic of pick_next_pushable_task(). > > Looking at the original patch, I don't see how it changes the semantics > (although mine may have). The original patch was: > > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1729,7 +1729,7 @@ static int pull_rt_task(struct rq *this_rq) > /* > * Are there still pullable RT tasks? > */ > - if (src_rq->rt.rt_nr_running <= 1) > + if (!has_pushable_tasks(src_rq)) > goto skip; > > p = pick_next_highest_task_rt(src_rq, this_cpu); > > And I still don't see a problem with this. If a rq has no pushable > tasks, then we shouldn't bother trying to pull from it (no task can > migrate). > > Thus, the original patch, I believe should be applied without question. > > Now, about my patch, the one that made pick_next_highest_task_rt into > just: > > static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu) > { > struct plist_head *head = &rq->rt.pushable_tasks; > struct task_struct *next; > > plist_for_each_entry(next, head, pushable_tasks) { > if (pick_rt_task(rq, next, cpu)) > return next; > } > > return NULL; > } > > You said could pick a task from a throttled rq. I'm not sure that is > different than what we have now. As the current > pick_next_highest_task_rt() just does a loop over the leaf_rt_rqs which > includes throttled rqs. That's because a throttled rq will not dequeue > the rt_rq from the leaf_rt_rq list if the rt_rq has rt_nr_running != 0.
Yes, there is no connection between logic of pushable tasks and throttling at the moment. These activities are independent. ( I tried to connect them at the patch: http://lkml.indiana.edu/hypermail/linux/kernel/1211.2/03750.html )
I think, there is no problem.
Kirill
> > I'm still thinking about adding both patches. > > -- Steve > >> Thanks, >> Yong >>> Kirill >>>>> ?Peter, do you see anything wrong with this patch? >>>>> >>>>> ?-- Steve >>>>> >>>>> ?diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c >>>>> ?index 61e3086..b44fd1b 100644 >>>>> ?--- a/kernel/sched/rt.c >>>>> ?+++ b/kernel/sched/rt.c >>>>> ?@@ -1416,39 +1416,15 @@ static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu) >>>>> ??/* Return the second highest RT task, NULL otherwise */ >>>>> ??static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu) >>>>> ??{ >>>>> ?- struct task_struct *next = NULL; >>>>> ?- struct sched_rt_entity *rt_se; >>>>> ?- struct rt_prio_array *array; >>>>> ?- struct rt_rq *rt_rq; >>>>> ?- int idx; >>>>> ?+ struct plist_head *head = &rq->rt.pushable_tasks; >>>>> ?+ struct task_struct *next; >>>>> >>>>> ?- for_each_leaf_rt_rq(rt_rq, rq) { >>>>> ?- array = &rt_rq->active; >>>>> ?- idx = sched_find_first_bit(array->bitmap); >>>>> ?-next_idx: >>>>> ?- if (idx >= MAX_RT_PRIO) >>>>> ?- continue; >>>>> ?- if (next && next->prio <= idx) >>>>> ?- continue; >>>>> ?- list_for_each_entry(rt_se, array->queue + idx, run_list) { >>>>> ?- struct task_struct *p; >>>>> ?- >>>>> ?- if (!rt_entity_is_task(rt_se)) >>>>> ?- continue; >>>>> ?- >>>>> ?- p = rt_task_of(rt_se); >>>>> ?- if (pick_rt_task(rq, p, cpu)) { >>>>> ?- next = p; >>>>> ?- break; >>>>> ?- } >>>>> ?- } >>>>> ?- if (!next) { >>>>> ?- idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1); >>>>> ?- goto next_idx; >>>>> ?- } >>>>> ?+ plist_for_each_entry(next, head, pushable_tasks) { >>>>> ?+ if (pick_rt_task(rq, next, cpu)) >>>>> ?+ return next; >>>>> ??????????} >>>>> >>>>> ?- return next; >>>>> ?+ return NULL; >>>>> ??} >>>>> >>>>> ??static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask); >>>>> >>>>> ?-- >>>>> ?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/ >>>> -- >>>> Only stand for myself >>> -- >>> 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/ -- 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/
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