linux-kernel - [PATCH 08/12] timer: Reuse next expiry cache after nohz exit

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Message-Id: <20200717140551.29076-9-frederic@kernel.org>
Date:   Fri, 17 Jul 2020 16:05:47 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: [PATCH 08/12] timer: Reuse next expiry cache after nohz exit

Now that we track the next expiry unconditionally when a timer is added,
we can reuse that information on a tick firing after exiting nohz.

Tested-by: Juri Lelli <juri.lelli@...hat.com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: Juri Lelli <juri.lelli@...hat.com>
---
 kernel/time/timer.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 76fd9644638b..13f48ee708aa 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1706,13 +1706,11 @@ static int collect_expired_timers(struct timer_base *base,
 	 * the next expiring timer.
 	 */
 	if ((long)(now - base->clk) > 2) {
-		unsigned long next = __next_timer_interrupt(base);
-
 		/*
 		 * If the next timer is ahead of time forward to current
 		 * jiffies, otherwise forward to the next expiry time:
 		 */
-		if (time_after(next, now)) {
+		if (time_after(base->next_expiry, now)) {
 			/*
 			 * The call site will increment base->clk and then
 			 * terminate the expiry loop immediately.
@@ -1720,7 +1718,7 @@ static int collect_expired_timers(struct timer_base *base,
 			base->clk = now;
 			return 0;
 		}
-		base->clk = next;
+		base->clk = base->next_expiry;
 	}
 	return __collect_expired_timers(base, heads);
 }
-- 
2.26.2