On Tue, 14 Nov 2017 09:57:11 -0800
Randy Dunlap <rdun...@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 <rdun...@infradead.org>
> > Signed-off-by: Stephen Hemminger <step...@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.
