sched/deadline: Remove the sysctl_sched_dl knobs

Remove the deadline specific sysctls for now. The problem with them is
that the interaction with the exisiting rt knobs is nearly impossible
to get right.

The current (as per before this patch) situation is that the rt and dl
bandwidth is completely separate and we enforce rt+dl < 100%. This is
undesirable because this means that the rt default of 95% leaves us
hardly any room, even though dl tasks are saver than rt tasks.

Another proposed solution was (a discarted patch) to have the dl
bandwidth be a fraction of the rt bandwidth. This is highly
confusing imo.

Furthermore neither proposal is consistent with the situation we
actually want; which is rt tasks ran from a dl server. In which case
the rt bandwidth is a direct subset of dl.

So whichever way we go, the introduction of dl controls at this point
is painful. Therefore remove them and instead share the rt budget.

This means that for now the rt knobs are used for dl admission control
and the dl runtime is accounted against the rt runtime. I realise that
this isn't entirely desirable either; but whatever we do we appear to
need to change the interface later, so better have a small interface
for now.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-zpyqbqds1r0vyxtxza1e7rdc@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 25 insertions, 2 deletions

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0c6b1d089cd4..ee25361becdd 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -63,10 +63,10 @@ void init_dl_bw(struct dl_bw *dl_b)
 {
 	raw_spin_lock_init(&dl_b->lock);
 	raw_spin_lock(&def_dl_bandwidth.dl_runtime_lock);
-	if (global_dl_runtime() == RUNTIME_INF)
+	if (global_rt_runtime() == RUNTIME_INF)
 		dl_b->bw = -1;
 	else
-		dl_b->bw = to_ratio(global_dl_period(), global_dl_runtime());
+		dl_b->bw = to_ratio(global_rt_period(), global_rt_runtime());
 	raw_spin_unlock(&def_dl_bandwidth.dl_runtime_lock);
 	dl_b->total_bw = 0;
 }
@@ -612,6 +612,29 @@ static void update_curr_dl(struct rq *rq)
 		if (!is_leftmost(curr, &rq->dl))
 			resched_task(curr);
 	}
+
+	/*
+	 * Because -- for now -- we share the rt bandwidth, we need to
+	 * account our runtime there too, otherwise actual rt tasks
+	 * would be able to exceed the shared quota.
+	 *
+	 * Account to the root rt group for now.
+	 *
+	 * The solution we're working towards is having the RT groups scheduled
+	 * using deadline servers -- however there's a few nasties to figure
+	 * out before that can happen.
+	 */
+	if (rt_bandwidth_enabled()) {
+		struct rt_rq *rt_rq = &rq->rt;
+
+		raw_spin_lock(&rt_rq->rt_runtime_lock);
+		rt_rq->rt_time += delta_exec;
+		/*
+		 * We'll let actual RT tasks worry about the overflow here, we
+		 * have our own CBS to keep us inline -- see above.
+		 */
+		raw_spin_unlock(&rt_rq->rt_runtime_lock);
+	}
 }
 
 #ifdef CONFIG_SMP