[RFCv5 PATCH 41/46] sched/fair: add triggers for OPP change requests

[Morten Rasmussen]

From: Juri Lelli <juri.lelli@xxxxxxx>

Each time a task is {en,de}queued we might need to adapt the current
frequency to the new usage. Add triggers on {en,de}queue_task_fair() for
this purpose.  Only trigger a freq request if we are effectively waking up
or going to sleep.  Filter out load balancing related calls to reduce the
number of triggers.

cc: Ingo Molnar <mingo@xxxxxxxxxx>
cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Signed-off-by: Juri Lelli <juri.lelli@xxxxxxx>
---
 kernel/sched/fair.c | 42 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f74e9d2..b8627c6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4281,7 +4281,10 @@ static inline void hrtick_update(struct rq *rq)
 }
 #endif
 
+static unsigned int capacity_margin = 1280; /* ~20% margin */
+
 static bool cpu_overutilized(int cpu);
+static unsigned long get_cpu_usage(int cpu);
 struct static_key __sched_energy_freq __read_mostly = STATIC_KEY_INIT_FALSE;
 
 /*
@@ -4332,6 +4335,26 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 		if (!task_new && !rq->rd->overutilized &&
 		    cpu_overutilized(rq->cpu))
 			rq->rd->overutilized = true;
+		/*
+		 * We want to trigger a freq switch request only for tasks that
+		 * are waking up; this is because we get here also during
+		 * load balancing, but in these cases it seems wise to trigger
+		 * as single request after load balancing is done.
+		 *
+		 * XXX: how about fork()? Do we need a special flag/something
+		 *      to tell if we are here after a fork() (wakeup_task_new)?
+		 *
+		 * Also, we add a margin (same ~20% used for the tipping point)
+		 * to our request to provide some head room if p's utilization
+		 * further increases.
+		 */
+		if (sched_energy_freq() && !task_new) {
+			unsigned long req_cap = get_cpu_usage(cpu_of(rq));
+
+			req_cap = req_cap * capacity_margin
+					>> SCHED_CAPACITY_SHIFT;
+			cpufreq_sched_set_cap(cpu_of(rq), req_cap);
+		}
 	}
 	hrtick_update(rq);
 }
@@ -4393,6 +4416,23 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	if (!se) {
 		sub_nr_running(rq, 1);
 		update_rq_runnable_avg(rq, 1);
+		/*
+		 * We want to trigger a freq switch request only for tasks that
+		 * are going to sleep; this is because we get here also during
+		 * load balancing, but in these cases it seems wise to trigger
+		 * as single request after load balancing is done.
+		 *
+		 * Also, we add a margin (same ~20% used for the tipping point)
+		 * to our request to provide some head room if p's utilization
+		 * further increases.
+		 */
+		if (sched_energy_freq() && task_sleep) {
+			unsigned long req_cap = get_cpu_usage(cpu_of(rq));
+
+			req_cap = req_cap * capacity_margin
+					>> SCHED_CAPACITY_SHIFT;
+			cpufreq_sched_set_cap(cpu_of(rq), req_cap);
+		}
 	}
 	hrtick_update(rq);
 }
@@ -4959,8 +4999,6 @@ static int find_new_capacity(struct energy_env *eenv,
 	return idx;
 }
 
-static unsigned int capacity_margin = 1280; /* ~20% margin */
-
 static bool cpu_overutilized(int cpu)
 {
 	return (capacity_of(cpu) * 1024) <
-- 
1.9.1

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