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Commit b6fe34d9 authored by Yunfeng Ye's avatar Yunfeng Ye Committed by Greg Kroah-Hartman
Browse files

tick/sched: Reduce seqcount held scope in tick_do_update_jiffies64() 



[ Upstream commit 94ad2e3cedb82af034f6d97c58022f162b669f9b ]

If jiffies are up to date already (caller lost the race against another
CPU) there is no point to change the sequence count. Doing that just forces
other CPUs into the seqcount retry loop in tick_nohz_next_event() for
nothing.

Just bail out early.

[ tglx: Rewrote most of it ]

Signed-off-by: default avatarYunfeng Ye <yeyunfeng@huawei.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201117132006.462195901@linutronix.de


Stable-dep-of: e9523a0d8189 ("tick/common: Align tick period with the HZ tick.")
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 746eac77

kernel/time/tick-sched.c

+22 −25
Original line number Diff line number Diff line
@@ -84,17 +84,18 @@ static void tick_do_update_jiffies64(ktime_t now) 


	/* Reevaluate with jiffies_lock held */

	raw_spin_lock(&jiffies_lock);

	write_seqcount_begin(&jiffies_seq);

	if (ktime_before(now, tick_next_period)) {

		raw_spin_unlock(&jiffies_lock);

		return;

	}



	delta = ktime_sub(now, last_jiffies_update);

	if (delta >= tick_period) {

	write_seqcount_begin(&jiffies_seq);



		delta = ktime_sub(delta, tick_period);

		last_jiffies_update = ktime_add(last_jiffies_update,

						tick_period);

	last_jiffies_update = ktime_add(last_jiffies_update, tick_period);



		/* Slow path for long timeouts */

	delta = ktime_sub(now, tick_next_period);

	if (unlikely(delta >= tick_period)) {

		/* Slow path for long idle sleep times */

		s64 incr = ktime_to_ns(tick_period);



		ticks = ktime_divns(delta, incr);
@@ -102,20 +103,16 @@ static void tick_do_update_jiffies64(ktime_t now) 
		last_jiffies_update = ktime_add_ns(last_jiffies_update,

						   incr * ticks);

	}



	do_timer(++ticks);



	/*

		 * Keep the tick_next_period variable up to date.

		 * WRITE_ONCE() pairs with the READ_ONCE() in the lockless

		 * quick check above.

	 * Keep the tick_next_period variable up to date.  WRITE_ONCE()

	 * pairs with the READ_ONCE() in the lockless quick check above.

	 */

	WRITE_ONCE(tick_next_period,

		   ktime_add(last_jiffies_update, tick_period));

	} else {

		write_seqcount_end(&jiffies_seq);

		raw_spin_unlock(&jiffies_lock);

		return;

	}



	write_seqcount_end(&jiffies_seq);

	raw_spin_unlock(&jiffies_lock);

	update_wall_time();