sched: Provide tunable to switch between PELT and window-based stats

Provide a runtime tunable to switch between using PELT-based load
stats and window-based load stats. This will be needed for runtime
analysis of the two load tracking schemes.

Change-Id: I018f6a90b49844bf2c4e5666912621d87acc7217
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>

kernel/sched/core.c

@@ -1752,10 +1752,10 @@ static inline void ttwu_activate(struct rq *rq, struct task_struct *p, int en_fl
 __read_mostly unsigned int sched_ravg_window = 10000000;
 
 /* Min window size (in ns) = 10ms */
-__read_mostly unsigned int min_sched_ravg_window = 10000000;
+#define MIN_SCHED_RAVG_WINDOW 10000000
 
 /* Max window size (in ns) = 1s */
-__read_mostly unsigned int max_sched_ravg_window = 1000000000;
+#define MAX_SCHED_RAVG_WINDOW 1000000000
 
 #define WINDOW_STATS_USE_RECENT        0
 #define WINDOW_STATS_USE_MAX   1
@@ -1764,6 +1764,9 @@ __read_mostly unsigned int max_sched_ravg_window = 1000000000;
 __read_mostly unsigned int sysctl_sched_window_stats_policy =
 	WINDOW_STATS_USE_AVG;
 
+/* 1 -> use PELT based load stats, 0 -> use window-based load stats */
+unsigned int __read_mostly sched_use_pelt = 1;
+
 unsigned int max_possible_efficiency = 1024;
 unsigned int min_possible_efficiency = 1024;
 
@@ -1832,6 +1835,9 @@ static int __init set_sched_ravg_window(char *str)
 {
 	get_option(&str, &sched_ravg_window);
 
+	sched_use_pelt = (sched_ravg_window < MIN_SCHED_RAVG_WINDOW ||
+				sched_ravg_window > MAX_SCHED_RAVG_WINDOW);
+
 	return 0;
 }
 
@@ -1843,7 +1849,7 @@ void update_task_ravg(struct task_struct *p, struct rq *rq, int update_sum)
 	int new_window;
 	u64 wallclock = sched_clock();
 
-	if (is_idle_task(p) || (sched_ravg_window < min_sched_ravg_window))
+	if (is_idle_task(p) || sched_use_pelt)
 		return;
 
 	do {

kernel/sched/fair.c

@@ -2545,12 +2545,18 @@ unsigned int __read_mostly sysctl_sched_init_task_load_pct = 100;
 
 static inline unsigned int task_load(struct task_struct *p)
 {
-	return p->se.avg.runnable_avg_sum_scaled;
+	if (sched_use_pelt)
+		return p->se.avg.runnable_avg_sum_scaled;
+
+	return p->ravg.demand;
 }
 
 static inline unsigned int max_task_load(void)
 {
-	return LOAD_AVG_MAX;
+	if (sched_use_pelt)
+		return LOAD_AVG_MAX;
+
+	return sched_ravg_window;
 }
 
 #endif /* CONFIG_SCHED_FREQ_INPUT || CONFIG_SCHED_HMP */

kernel/sched/sched.h

@@ -930,6 +930,7 @@ extern void init_new_task_load(struct task_struct *p);
 #if defined(CONFIG_SCHED_FREQ_INPUT) || defined(CONFIG_SCHED_HMP)
 
 extern unsigned int sched_ravg_window;
+extern unsigned int sched_use_pelt;
 extern unsigned int max_possible_freq;
 extern unsigned int min_max_freq;
 extern unsigned int pct_task_load(struct task_struct *p);
@@ -949,13 +950,21 @@ extern unsigned int sched_init_task_load_windows;
 static inline void
 inc_cumulative_runnable_avg(struct rq *rq, struct task_struct *p)
 {
-	rq->cumulative_runnable_avg += p->ravg.demand;
+	if (sched_use_pelt)
+		rq->cumulative_runnable_avg +=
+				p->se.avg.runnable_avg_sum_scaled;
+	else
+		rq->cumulative_runnable_avg += p->ravg.demand;
 }
 
 static inline void
 dec_cumulative_runnable_avg(struct rq *rq, struct task_struct *p)
 {
-	rq->cumulative_runnable_avg -= p->ravg.demand;
+	if (sched_use_pelt)
+		rq->cumulative_runnable_avg -=
+				p->se.avg.runnable_avg_sum_scaled;
+	else
+		rq->cumulative_runnable_avg -= p->ravg.demand;
 	BUG_ON((s64)rq->cumulative_runnable_avg < 0);
 }