sched/fair: Consider missed ticks in NOHZ_FULL in update_cpu_load_nohz()

Usually the tick can be stopped for an idle CPU in NOHZ. However in NOHZ_FULL
mode, a non-idle CPU's tick can also 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@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1447115762-19734-3-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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);

kernel/sched/fair.c

@@ -4397,10 +4397,11 @@ 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)
@@ -4411,10 +4412,11 @@ 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);
 }

kernel/time/tick-sched.c

@@ -694,11 +694,11 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
 	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);
 	}