Skip to contentSkip to conversation

netem: fix compilation on 32 bit

PATCH In review Stephen Hemminger 5 participants 7 messages Nov 14, 2017 – Nov 15, 2017

Subsystems (4)
Networking Network drivers Traffic control (tc) Netem network emulator
lore
Share & tools
lore

Stephen Hemminger

author maintainer
#0 lore raw

v2 cover netem: fix compilation on 32 bit

A couple of places where 64 bit CPU was being assumed incorrectly.

Stephen Hemminger (2):
netem: fix 64 bit divide
netem: remove unnecessary 64 bit modulus

 net/sched/sch_netem.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)
Signature · 1 line
2.11.0
author maintainer
#1 lore raw

PATCH v2 1/2 netem: use 64 bit divide by rate

Since times are now expressed in nanosecond, need to now do true 64 bit divide. Old code would truncate rate at 32 bits. Rename function to better express current usage.

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;
Signature · 1 line
2.11.0
author maintainer
#2 lore raw

PATCH v2 2/2 netem: remove unnecessary 64 bit modulus

In reply to Stephen Hemminger

Fix compilation on 32 bit platforms (where doing modulus operation with 64 bit requires extra glibc functions) by truncation. The jitter for table distribution is limited to a 32 bit value because random numbers are scaled as 32 bit value.

Also fix some whitespace.

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 | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
net/sched/sch_netem.c +3 -3
index 644323d6081c..dd70924cbcdf 100644
@@ -312,9 +312,9 @@ static bool loss_event(struct netem_sched_data *q)
  * std deviation sigma.  Uses table lookup to approximate the desired
  * distribution, and a uniformly-distributed pseudo-random source.
  */
-static s64 tabledist(s64 mu, s64 sigma,
+static s64 tabledist(s64 mu, s32 sigma,
 		     struct crndstate *state,
-			 const struct disttable *dist)
+		     const struct disttable *dist)
 {
 	s64 x;
 	long t;

@@ -327,7 +327,7 @@ static s64 tabledist(s64 mu, s64 sigma,
 
 	/* default uniform distribution */
 	if (dist == NULL)
-		return (rnd % (2*sigma)) - sigma + mu;
+		return (rnd % (2 * sigma)) - sigma + mu;
 
 	t = dist->table[rnd % dist->size];
 	x = (sigma % NETEM_DIST_SCALE) * t;
Signature · 1 line
2.11.0
Acked-by on the v2 series
#3 lore raw
In reply to Stephen Hemminger
Quoted 9 lines · Stephen Hemminger

A couple of places where 64 bit CPU was being assumed incorrectly.

Stephen Hemminger (2):
netem: fix 64 bit divide
netem: remove unnecessary 64 bit modulus

 net/sched/sch_netem.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)
Acked-by Randy Dunlap <[email protected]>

Thanks.

Signature · 1 line
~Randy
Acked-by
#4 lore raw
Quoted 7 lines · Randy Dunlap
Quoted 6 lines · Stephen Hemminger

A couple of places where 64 bit CPU was being assumed incorrectly.

Stephen Hemminger (2):
netem: fix 64 bit divide
netem: remove unnecessary 64 bit modulus

Quoted 5 lines
Quoted 3 lines
 net/sched/sch_netem.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)
Acked-by Randy Dunlap <[email protected]>
Acked-by Dave Taht <[email protected]>

Thx.

Tested-by on the v2 series
#5 lore raw
In reply to Stephen Hemminger
Quoted 10 lines · Stephen Hemminger

A couple of places where 64 bit CPU was being assumed incorrectly.

Stephen Hemminger (2):
netem: fix 64 bit divide
netem: remove unnecessary 64 bit modulus

 net/sched/sch_netem.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)
Acked-by Randy Dunlap <[email protected]>
Acked-by Dave Taht <[email protected]>

These appears to fix the MIPS build, so

Tested-by James Hogan <[email protected]>

Thanks
James