* [PATCH] netem: fix 64 bit divide
@ 2017-11-14 17:28 Stephen Hemminger
2017-11-14 17:57 ` Randy Dunlap
0 siblings, 1 reply; 3+ messages in thread
From: Stephen Hemminger @ 2017-11-14 17:28 UTC (permalink / raw)
To: davem, dave.taht, rdunlap; +Cc: netdev, Stephen Hemminger, 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 <rdunlap@infradead.org>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
net/sched/sch_netem.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index b686e755fda9..644323d6081c 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -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;
--
2.11.0
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] netem: fix 64 bit divide
2017-11-14 17:28 [PATCH] netem: fix 64 bit divide Stephen Hemminger
@ 2017-11-14 17:57 ` Randy Dunlap
2017-11-14 19:09 ` Stephen Hemminger
0 siblings, 1 reply; 3+ messages in thread
From: Randy Dunlap @ 2017-11-14 17:57 UTC (permalink / raw)
To: Stephen Hemminger, davem, dave.taht; +Cc: netdev, Stephen Hemminger
On 11/14/2017 09:28 AM, Stephen Hemminger wrote:
> 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 <rdunlap@infradead.org>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
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().
> ---
> net/sched/sch_netem.c | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> index b686e755fda9..644323d6081c 100644
> --- a/net/sched/sch_netem.c
> +++ b/net/sched/sch_netem.c
> @@ -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;
>
--
~Randy
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] netem: fix 64 bit divide
2017-11-14 17:57 ` Randy Dunlap
@ 2017-11-14 19:09 ` Stephen Hemminger
0 siblings, 0 replies; 3+ messages in thread
From: Stephen Hemminger @ 2017-11-14 19:09 UTC (permalink / raw)
To: Randy Dunlap; +Cc: davem, dave.taht, netdev, Stephen Hemminger
On Tue, 14 Nov 2017 09:57:11 -0800
Randy Dunlap <rdunlap@infradead.org> wrote:
> On 11/14/2017 09:28 AM, Stephen Hemminger wrote:
> > 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 <rdunlap@infradead.org>
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
>
> 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().
>
> > ---
> > net/sched/sch_netem.c | 11 ++++-------
> > 1 file changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> > index b686e755fda9..644323d6081c 100644
> > --- a/net/sched/sch_netem.c
> > +++ b/net/sched/sch_netem.c
> > @@ -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;
> >
>
>
Close, the problem is here:
return (rnd % (2*sigma)) - sigma + mu;
139d: 8b 4d dc mov -0x24(%ebp),%ecx
13a0: 8b 5d e0 mov -0x20(%ebp),%ebx
13a3: 0f a4 cb 01 shld $0x1,%ecx,%ebx
13a7: 01 c9 add %ecx,%ecx
13a9: 53 push %ebx
13aa: 51 push %ecx
13ab: e8 fc ff ff ff call 13ac <netem_enqueue+0x9dc>
13ac: R_386_PC32 __moddi3
Will add second patch for that.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-11-14 17:28 [PATCH] netem: fix 64 bit divide Stephen Hemminger
2017-11-14 17:57 ` Randy Dunlap
2017-11-14 19:09 ` Stephen Hemminger
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