From 93c43008368d60f2cb11cc239a3219a2f4142c30 Mon Sep 17 00:00:00 2001 From: Yunfeng Ye Date: Tue, 17 Nov 2020 14:19:46 +0100 Subject: [PATCH] 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: Yunfeng Ye Signed-off-by: Thomas Gleixner 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 --- kernel/time/tick-sched.c | 55 +++++++++++++++++++--------------------- 1 file changed, 26 insertions(+), 29 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 4f1b6170b3a2..ac9953f6f92c 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); - write_seqcount_begin(&jiffies_seq); - - delta = ktime_sub(now, last_jiffies_update); - if (delta >= tick_period) { - - delta = ktime_sub(delta, tick_period); - last_jiffies_update = ktime_add(last_jiffies_update, - tick_period); - - /* Slow path for long timeouts */ - if (unlikely(delta >= tick_period)) { - s64 incr = ktime_to_ns(tick_period); - - ticks = ktime_divns(delta, incr); - - 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. - */ - WRITE_ONCE(tick_next_period, - ktime_add(last_jiffies_update, tick_period)); - } else { - write_seqcount_end(&jiffies_seq); + if (ktime_before(now, tick_next_period)) { raw_spin_unlock(&jiffies_lock); return; } + + write_seqcount_begin(&jiffies_seq); + + 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); + + ticks = ktime_divns(delta, incr); + + 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. + */ + WRITE_ONCE(tick_next_period, + ktime_add(last_jiffies_update, tick_period)); + write_seqcount_end(&jiffies_seq); raw_spin_unlock(&jiffies_lock); update_wall_time();