netdev - [PATCH v2 net-next 2/3] net_sched: do not reprogram a timer about to expire

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Date:   Mon, 16 Mar 2020 19:12:50 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH v2 net-next 2/3] net_sched: do not reprogram a timer about to expire

qdisc_watchdog_schedule_range_ns() can use the newly added slack
and avoid rearming the hrtimer a bit earlier than the current
value. This patch has no effect if delta_ns parameter
is zero.

Note that this means the max slack is potentially doubled.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/sched/sch_api.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 83984be04f57d93b4efc50bb9cf390b116101fdd..0d99df1e764db812f5dfc78a9c54832c0f676f70 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -625,8 +625,13 @@ void qdisc_watchdog_schedule_range_ns(struct qdisc_watchdog *wd, u64 expires,
 		     &qdisc_root_sleeping(wd->qdisc)->state))
 		return;
 
-	if (wd->last_expires == expires)
-		return;
+	if (hrtimer_is_queued(&wd->timer)) {
+		/* If timer is already set in [expires, expires + delta_ns],
+		 * do not reprogram it.
+		 */
+		if (wd->last_expires - expires <= delta_ns)
+			return;
+	}
 
 	wd->last_expires = expires;
 	hrtimer_start_range_ns(&wd->timer,
-- 
2.25.1.481.gfbce0eb801-goog