net: sched: remove qdisc_watchdog->last_expires

This field mirrors hrtimer softexpires, we can instead
use the existing helpers.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230308182648.1150762-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/pkt_sched.h

@@ -64,7 +64,6 @@ static inline psched_time_t psched_get_time(void)
 }
 
 struct qdisc_watchdog {
-	u64		last_expires;
 	struct hrtimer	timer;
 	struct Qdisc	*qdisc;
 };

net/sched/sch_api.c

@@ -639,14 +639,16 @@ void qdisc_watchdog_schedule_range_ns(struct qdisc_watchdog *wd, u64 expires,
 		return;
 
 	if (hrtimer_is_queued(&wd->timer)) {
+		u64 softexpires;
+
+		softexpires = ktime_to_ns(hrtimer_get_softexpires(&wd->timer));
 		/* If timer is already set in [expires, expires + delta_ns],
 		 * do not reprogram it.
 		 */
-		if (wd->last_expires - expires <= delta_ns)
+		if (softexpires - expires <= delta_ns)
 			return;
 	}
 
-	wd->last_expires = expires;
 	hrtimer_start_range_ns(&wd->timer,
 			       ns_to_ktime(expires),
 			       delta_ns,