From: Yunfeng Ye yeyunfeng@huawei.com
[ 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: Yunfeng Ye yeyunfeng@huawei.com Signed-off-by: Thomas 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: Sasha Levin sashal@kernel.org --- kernel/time/tick-sched.c | 47 +++++++++++++++++++--------------------- 1 file changed, 22 insertions(+), 25 deletions(-)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 1dfa53494164a..eaeeb4bb1f8ab 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -84,38 +84,35 @@ static void tick_do_update_jiffies64(ktime_t now)
/* Reevaluate with jiffies_lock held */ raw_spin_lock(&jiffies_lock); + if (ktime_before(now, tick_next_period)) { + raw_spin_unlock(&jiffies_lock); + return; + } + write_seqcount_begin(&jiffies_seq);
- delta = ktime_sub(now, last_jiffies_update); - if (delta >= tick_period) { + last_jiffies_update = ktime_add(last_jiffies_update, tick_period);
- delta = ktime_sub(delta, tick_period); - last_jiffies_update = ktime_add(last_jiffies_update, - tick_period); + 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);
- /* Slow path for long timeouts */ - if (unlikely(delta >= tick_period)) { - s64 incr = ktime_to_ns(tick_period); + ticks = ktime_divns(delta, incr);
- ticks = ktime_divns(delta, incr); + last_jiffies_update = ktime_add_ns(last_jiffies_update, + incr * ticks); + }
- last_jiffies_update = ktime_add_ns(last_jiffies_update, - incr * ticks); - } - do_timer(++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. + */ + WRITE_ONCE(tick_next_period, + ktime_add(last_jiffies_update, tick_period));
- /* - * 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();