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Commit 15934a37 authored by Guillaume Chazarain's avatar Guillaume Chazarain Committed by Ingo Molnar
Browse files

sched: fix rq->clock overflows detection with CONFIG_NO_HZ 



When using CONFIG_NO_HZ, rq->tick_timestamp is not updated every TICK_NSEC.
We check that the number of skipped ticks matches the clock jump seen in
__update_rq_clock().

Signed-off-by: default avatarGuillaume Chazarain <guichaz@yahoo.fr>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 30914a58

kernel/sched.c

+35 −3
Original line number Diff line number Diff line
@@ -397,6 +397,7 @@ struct rq { 
	unsigned long cpu_load[CPU_LOAD_IDX_MAX];

	unsigned char idle_at_tick;

#ifdef CONFIG_NO_HZ

	unsigned long last_tick_seen;

	unsigned char in_nohz_recently;

#endif

	/* capture load from *all* tasks on this cpu: */
@@ -500,6 +501,32 @@ static inline int cpu_of(struct rq *rq) 
#endif

}



#ifdef CONFIG_NO_HZ

static inline bool nohz_on(int cpu)

{

	return tick_get_tick_sched(cpu)->nohz_mode != NOHZ_MODE_INACTIVE;

}



static inline u64 max_skipped_ticks(struct rq *rq)

{

	return nohz_on(cpu_of(rq)) ? jiffies - rq->last_tick_seen + 2 : 1;

}



static inline void update_last_tick_seen(struct rq *rq)

{

	rq->last_tick_seen = jiffies;

}

#else

static inline u64 max_skipped_ticks(struct rq *rq)

{

	return 1;

}



static inline void update_last_tick_seen(struct rq *rq)

{

}

#endif



/*

 * Update the per-runqueue clock, as finegrained as the platform can give

 * us, but without assuming monotonicity, etc.:
@@ -524,9 +551,12 @@ static void __update_rq_clock(struct rq *rq) 
		/*

		 * Catch too large forward jumps too:

		 */

		if (unlikely(clock + delta > rq->tick_timestamp + TICK_NSEC)) {

			if (clock < rq->tick_timestamp + TICK_NSEC)

				clock = rq->tick_timestamp + TICK_NSEC;

		u64 max_jump = max_skipped_ticks(rq) * TICK_NSEC;

		u64 max_time = rq->tick_timestamp + max_jump;



		if (unlikely(clock + delta > max_time)) {

			if (clock < max_time)

				clock = max_time;

			else

				clock++;

			rq->clock_overflows++;
@@ -3812,6 +3842,7 @@ void scheduler_tick(void) 
		rq->clock_underflows++;

	}

	rq->tick_timestamp = rq->clock;

	update_last_tick_seen(rq);

	update_cpu_load(rq);

	curr->sched_class->task_tick(rq, curr, 0);

	update_sched_rt_period(rq);
@@ -7261,6 +7292,7 @@ void __init sched_init(void) 
		lockdep_set_class(&rq->lock, &rq->rq_lock_key);

		rq->nr_running = 0;

		rq->clock = 1;

		update_last_tick_seen(rq);

		init_cfs_rq(&rq->cfs, rq);

		init_rt_rq(&rq->rt, rq);

#ifdef CONFIG_FAIR_GROUP_SCHED