[PATCH v5 2/2] sched: make update_cpu_load_nohz() consider missed ticks in NOHZ_FULL

[byungchul.park]

From: Byungchul Park <byungchul.park@xxxxxxx>

Usually tick can be stopped for an idle cpu in NOHZ. However in NOHZ_FULL,
a non-idle cpu's tick also can be stopped. However, update_cpu_load_nohz()
does not consider the case a non-idle cpu's tick has been stopped at all.

This patch makes the update_cpu_load_nohz() know if the calling path comes
from NOHZ_FULL or idle NOHZ.

Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
Acked-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
 include/linux/sched.h    |    4 ++--
 kernel/sched/fair.c      |   10 ++++++----
 kernel/time/tick-sched.c |    8 ++++----
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 699228b..f1b59aa 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -177,9 +177,9 @@ extern void get_iowait_load(unsigned long *nr_waiters, unsigned long *load);
 extern void calc_global_load(unsigned long ticks);
 
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
-extern void update_cpu_load_nohz(void);
+extern void update_cpu_load_nohz(int active);
 #else
-static inline void update_cpu_load_nohz(void) { }
+static inline void update_cpu_load_nohz(int active) { }
 #endif
 
 extern unsigned long get_parent_ip(unsigned long addr);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7760678..3d93756 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4419,10 +4419,11 @@ static void update_idle_cpu_load(struct rq *this_rq)
 /*
  * Called from tick_nohz_idle_exit() -- try and fix up the ticks we missed.
  */
-void update_cpu_load_nohz(void)
+void update_cpu_load_nohz(int active)
 {
 	struct rq *this_rq = this_rq();
 	unsigned long curr_jiffies = READ_ONCE(jiffies);
+	unsigned long load = active ? weighted_cpuload(cpu_of(this_rq)) : 0;
 	unsigned long pending_updates;
 
 	if (curr_jiffies == this_rq->last_load_update_tick)
@@ -4433,10 +4434,11 @@ void update_cpu_load_nohz(void)
 	if (pending_updates) {
 		this_rq->last_load_update_tick = curr_jiffies;
 		/*
-		 * We were idle, this means load 0, the current load might be
-		 * !0 due to remote wakeups and the sort.
+		 * In the regular NOHZ case, we were idle, this means load 0.
+		 * In the NOHZ_FULL case, we were non-idle, we should consider
+		 * its weighted load.
 		 */
-		__update_cpu_load(this_rq, 0, pending_updates, 0);
+		__update_cpu_load(this_rq, load, pending_updates, active);
 	}
 	raw_spin_unlock(&this_rq->lock);
 }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 7c7ec45..515edf3 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -694,11 +694,11 @@ out:
 	return tick;
 }
 
-static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
+static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now, int active)
 {
 	/* Update jiffies first */
 	tick_do_update_jiffies64(now);
-	update_cpu_load_nohz();
+	update_cpu_load_nohz(active);
 
 	calc_load_exit_idle();
 	touch_softlockup_watchdog();
@@ -725,7 +725,7 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts)
 	if (can_stop_full_tick())
 		tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
 	else if (ts->tick_stopped)
-		tick_nohz_restart_sched_tick(ts, ktime_get());
+		tick_nohz_restart_sched_tick(ts, ktime_get(), 1);
 #endif
 }
 
@@ -916,7 +916,7 @@ void tick_nohz_idle_exit(void)
 		tick_nohz_stop_idle(ts, now);
 
 	if (ts->tick_stopped) {
-		tick_nohz_restart_sched_tick(ts, now);
+		tick_nohz_restart_sched_tick(ts, now, 0);
 		tick_nohz_account_idle_ticks(ts);
 	}
 
-- 
1.7.9.5

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