On Mon, 2013-05-20 at 17:53 -0700, Eric Dumazet wrote:
> On Tue, 2013-05-21 at 01:28 +0100, Ben Hutchings wrote:
> > I'm seeing packet loss when forwarding from a LAN to PPP, whenever GRO
> > kicks in on the LAN interface.
> >
> > On Mon, 2013-05-20 at 05:48 +0100, Ben Hutchings wrote:
> > [...]
> > > The Windows system is connected to the LAN interface (int0). Turning
> > > off GRO on this interface works around the problem. But since GRO is
> > > on by default, it clearly ought to work properly with iptables.
> > >
> > > I'll try to work out where the drops are occurring, but the
> > > perf net_dropmonitor script is also broken...
> > [...]
> >
> > I've fixed that script and now I can see that it's not iptables but
> > tbf_enqueue() that is dropping the GRO'd packets. I do traffic-shaping
> > on the PPP link like this:
> >
> > tc qdisc replace dev ppp0 root tbf rate 420kbit latency 50ms burst 1540
> >
> > The local TCP will never generate an skb larger than the burst size
> > because it knows the PPP interface can't do GSO or TSO. And the wifi
> > network doesn't seem to be fast enough for GRO to have much of an
> > effect. But a peer on the wired network can trigger GRO and this
> > produces an skb that exceeds the burst size.
> >
> > Is this a bug in sch_tbf, or should I accept it as a limitation? It
> > seems like it should do GSO on entry to the queue if necessary.
> >
>
> This has been discussed on netdev this year.
>
> Jiri Pirko was working on this.
>
> (thread : tbf: take into account gso skbs)
I have tested the following (net-next) patch
diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index c8388f3..a132620 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -116,14 +116,50 @@ struct tbf_sched_data {
struct qdisc_watchdog watchdog; /* Watchdog timer */
};
+
+static int tbf_segment(struct sk_buff *skb, struct Qdisc *sch, struct Qdisc
*child)
+{
+ struct sk_buff *segs, *nskb;
+ netdev_features_t features = netif_skb_features(skb);
+ int ret, nb;
+
+ segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);
+
+ if (IS_ERR_OR_NULL(segs))
+ return qdisc_reshape_fail(skb, sch);
+
+ nb = 0;
+ while (segs) {
+ nskb = segs->next;
+ segs->next = NULL;
+ qdisc_skb_cb(segs)->pkt_len = segs->len;
+
+ ret = qdisc_enqueue(segs, child);
+ if (ret != NET_XMIT_SUCCESS) {
+ if (net_xmit_drop_count(ret))
+ sch->qstats.drops++;
+ } else {
+ nb++;
+ }
+ segs = nskb;
+ }
+ sch->q.qlen += nb;
+ if (nb > 1)
+ qdisc_tree_decrease_qlen(sch, 1 - nb);
+ consume_skb(skb);
+ return nb > 0 ? NET_XMIT_SUCCESS : NET_XMIT_DROP;
+}
+
static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
struct tbf_sched_data *q = qdisc_priv(sch);
int ret;
- if (qdisc_pkt_len(skb) > q->max_size)
+ if (qdisc_pkt_len(skb) > q->max_size) {
+ if (skb_is_gso(skb))
+ return tbf_segment(skb, sch, q->qdisc);
return qdisc_reshape_fail(skb, sch);
-
+ }
ret = qdisc_enqueue(skb, q->qdisc);
if (ret != NET_XMIT_SUCCESS) {
if (net_xmit_drop_count(ret))
--
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