Le Thursday 17 May 2018 à 11:32:06 (+0200), Peter Zijlstra a écrit :
> On Thu, May 17, 2018 at 11:05:30AM +0200, Peter Zijlstra wrote:
> > Hurm.. I think this is also wrong. See how dequeue_rt_stack() is also
> > called from the enqueue path. Also, nothing calls cpufreq_update_util()
> > on the throttle path now.

Yes I missed the point that rt_entities were dequeued then re-enqueued when
a task was either enqueued or dequeued.

That's also means that enqueue_top_rt_rq() is always called when a task is
enqueued or dequeued and also when groups are throttled or unthrottled
In fact, the only point where it's not called, is when root rt_rq is
throttled. So I have prepared the patch below which call cpufreq_update util
in enqueue_top_rt_rq() and also when we throttle the root rt_rq.
According to the tests I have done , it seems to work for enqueue/dequeue and
throttle/unthrottle use cases.

I have re-used your rt_rq_is_runnable() which takes into account rt_queued

---
 kernel/sched/cpufreq_schedutil.c |  2 +-
 kernel/sched/rt.c                | 16 ++++++++++------
 kernel/sched/sched.h             |  5 +++++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index e13df95..1751f96 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -185,7 +185,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu 
*sg_cpu)
        struct rq *rq = cpu_rq(sg_cpu->cpu);
        unsigned long util;
 
-       if (rq->rt.rt_nr_running) {
+       if (rt_rq_is_runnable(&rq->rt)) {
                util = sg_cpu->max;
        } else {
                util = sg_cpu->util_dl;
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7aef6b4..d6b9517 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -508,8 +508,11 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
 
        rt_se = rt_rq->tg->rt_se[cpu];
 
-       if (!rt_se)
+       if (!rt_se) {
                dequeue_top_rt_rq(rt_rq);
+               /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
+               cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
+       }
        else if (on_rt_rq(rt_se))
                dequeue_rt_entity(rt_se, 0);
 }
@@ -1001,8 +1004,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
        sub_nr_running(rq, rt_rq->rt_nr_running);
        rt_rq->rt_queued = 0;
 
-       /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-       cpufreq_update_util(rq, 0);
 }
 
 static void
@@ -1014,11 +1015,14 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
 
        if (rt_rq->rt_queued)
                return;
-       if (rt_rq_throttled(rt_rq) || !rt_rq->rt_nr_running)
+
+       if (rt_rq_throttled(rt_rq))
                return;
 
-       add_nr_running(rq, rt_rq->rt_nr_running);
-       rt_rq->rt_queued = 1;
+       if (rt_rq->rt_nr_running) {
+               add_nr_running(rq, rt_rq->rt_nr_running);
+               rt_rq->rt_queued = 1;
+       }
 
        /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
        cpufreq_update_util(rq, 0);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c9895d3..bbebcfe 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -609,6 +609,11 @@ struct rt_rq {
 #endif
 };
 
+static inline bool rt_rq_is_runnable(struct rt_rq *rt_rq)
+{
+       return rt_rq->rt_queued && rt_rq->rt_nr_running;
+}
+
 /* Deadline class' related fields in a runqueue */
 struct dl_rq {
        /* runqueue is an rbtree, ordered by deadline */
-- 
2.7.4





> > 
> > And talking about throttle; I think we wanted to check rt_queued in that
> > case.
> 
> Bah, clearly you also want to update on unthrottle.. but I think there's
> more buggered wrt throtteling.




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