[patch 01/48] sched/eevdf: Fix HRTICK duration

[Thomas Gleixner]

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

The nominal duration for an EEVDF task to run is until its deadline. At
which point the deadline is moved ahead and a new task selection is done.

Try and predict the time 'lost' to higher scheduling classes. Since this is
an estimate, the timer can be both early or late. In case it is early
task_tick_fair() will take the !need_resched() path and restarts the timer.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Reviewed-by: Juri Lelli <juri.lelli@xxxxxxxxxx>

---
 kernel/sched/fair.c |   43 ++++++++++++++++++++++++++++---------------
 1 file changed, 28 insertions(+), 15 deletions(-)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6735,21 +6735,37 @@ static inline void sched_fair_update_sto
 static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 {
 	struct sched_entity *se = &p->se;
+	unsigned long scale = 1024;
+	unsigned long util = 0;
+	u64 vdelta;
+	u64 delta;
 
 	WARN_ON_ONCE(task_rq(p) != rq);
 
-	if (rq->cfs.h_nr_queued > 1) {
-		u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
-		u64 slice = se->slice;
-		s64 delta = slice - ran;
-
-		if (delta < 0) {
-			if (task_current_donor(rq, p))
-				resched_curr(rq);
-			return;
-		}
-		hrtick_start(rq, delta);
+	if (rq->cfs.h_nr_queued <= 1)
+		return;
+
+	/*
+	 * Compute time until virtual deadline
+	 */
+	vdelta = se->deadline - se->vruntime;
+	if ((s64)vdelta < 0) {
+		if (task_current_donor(rq, p))
+			resched_curr(rq);
+		return;
 	}
+	delta = (se->load.weight * vdelta) / NICE_0_LOAD;
+
+	/*
+	 * Correct for instantaneous load of other classes.
+	 */
+	util += cpu_util_irq(rq);
+	if (util && util < 1024) {
+		scale *= 1024;
+		scale /= (1024 - util);
+	}
+
+	hrtick_start(rq, (scale * delta) / 1024);
 }
 
 /*
@@ -13365,11 +13381,8 @@ static void task_tick_fair(struct rq *rq
 		entity_tick(cfs_rq, se, queued);
 	}
 
-	if (queued) {
-		if (!need_resched())
-			hrtick_start_fair(rq, curr);
+	if (queued)
 		return;
-	}
 
 	if (static_branch_unlikely(&sched_numa_balancing))
 		task_tick_numa(rq, curr);