Tue, May 21, 2013 at 04:03:10AM CEST, eric.duma...@gmail.com wrote:
>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
This is looking good to me. On my test machine it makes tbf work correctly
with gso packets.
I worked on similar patch (enqueue path) myself some time ago but I got
distracted by other tasks.
Do you plan to submit this 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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