netem: fix 64 bit divide

Since times are now expressed in 64 bit nanosecond, need to now do true 64 bit divide. Change the name of the function to bette express the new units.

Fixes 99803171ef04 ("netem: add uapi to express delay and jitter in nanoseconds")

Reported-by Randy Dunlap <[email protected]>

Signed-off-by Stephen Hemminger <[email protected]>

---
 net/sched/sch_netem.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

net/sched/sch_netem.c +4 -7

index b686e755fda9..644323d6081c 100644
@@ -339,10 +339,8 @@ static s64 tabledist(s64 mu, s64 sigma,
 	return  x / NETEM_DIST_SCALE + (sigma / NETEM_DIST_SCALE) * t + mu;
 }
 
-static u64 packet_len_2_sched_time(unsigned int len,
-				   struct netem_sched_data *q)
+static u64 packet_time_ns(u64 len, const struct netem_sched_data *q)
 {
-	u64 offset;
 	len += q->packet_overhead;
 
 	if (q->cell_size) {

@@ -352,9 +350,8 @@ static u64 packet_len_2_sched_time(unsigned int len,
 			cells++;
 		len = cells * (q->cell_size + q->cell_overhead);
 	}
-	offset = (u64)len * NSEC_PER_SEC;
-	do_div(offset, q->rate);
-	return offset;
+
+	return div64_u64(len * NSEC_PER_SEC, q->rate);
 }
 
 static void tfifo_reset(struct Qdisc *sch)

@@ -556,7 +553,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 				now = last->time_to_send;
 			}
 
-			delay += packet_len_2_sched_time(qdisc_pkt_len(skb), q);
+			delay += packet_time_ns(qdisc_pkt_len(skb), q);
 		}
 
 		cb->time_to_send = now + delay;

Quoted 7 lines · Stephen Hemminger

Since times are now expressed in 64 bit nanosecond, need to now do true 64 bit divide. Change the name of the function to bette express the new units.

Fixes 99803171ef04 ("netem: add uapi to express delay and jitter in nanoseconds")

Reported-by Randy Dunlap <[email protected]>

Signed-off-by Stephen Hemminger <[email protected]>

Hi Stephen,

I still get it. Maybe it's this % operator:

		skb->data[prandom_u32() % skb_headlen(skb)] ^=
			1<<(prandom_u32() % 8);

in net_enqueue().

Quoted 36 lines

---
 net/sched/sch_netem.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

net/sched/sch_netem.c +3 -6

index b686e755fda9..644323d6081c 100644
@@ -339,10 +339,8 @@ static s64 tabledist(s64 mu, s64 sigma,
 	return  x / NETEM_DIST_SCALE + (sigma / NETEM_DIST_SCALE) * t + mu;
 }
 
-static u64 packet_len_2_sched_time(unsigned int len,
-				   struct netem_sched_data *q)
+static u64 packet_time_ns(u64 len, const struct netem_sched_data *q)
 {
-	u64 offset;
 	len += q->packet_overhead;
 
 	if (q->cell_size) {

@@ -352,9 +350,8 @@ static u64 packet_len_2_sched_time(unsigned int len,
 			cells++;
 		len = cells * (q->cell_size + q->cell_overhead);
 	}
-	offset = (u64)len * NSEC_PER_SEC;
-	do_div(offset, q->rate);
-	return offset;
+
+	return div64_u64(len * NSEC_PER_SEC, q->rate);
 }
 
 static void tfifo_reset(struct Qdisc *sch)

@@ -556,7 +553,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 				now = last->time_to_send;
 			}
 

net/sched/sch_netem.c static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch, · line 559

Quoted 6 lines

net/sched/sch_netem.c +1 -1

-			delay += packet_len_2_sched_time(qdisc_pkt_len(skb), q);
+			delay += packet_time_ns(qdisc_pkt_len(skb), q);
 		}
 
 		cb->time_to_send = now + delay;