From: Abdul Basit <abasit@xxxxxxxxx>
Date: Tue, 14 Oct 2008 21:37:04 -0400
[ netdev CC:'d, you'll reach more knowledgable people there ]
> I am running linux kernel 2.6.23.1 on PowerPC and trying to set qdisc tbf to limit the rate:-
> *
> *==> tc qdisc add dev eth0 root tbf rate 2048kbit buffer 10kb latency 50ms
>
> The problem is no matter what rate i specify, if I download a file it always get down to ~16-18Kbps download speed,
> after investigating a bit more, i found by tc -s qdisc show that many dropped packets show up in statistic s,
> looking further in kernel code, I found that in linux/net/sched/sch_tbf.c:126
>
> static int tbf_enqueue(struct sk_buff *skb, struct Qdisc* sch)
> {
> struct tbf_sched_data *q = qdisc_priv(sch);
> int ret;
> if (skb->len > q->max_size) {
> printk (KERN_INFO "tbf_enqueue, drop skb->len = %d, q->max_size = %d\n", skb->len, q->max_size);
> sch->qstats.drops++;
>
> ....
> }
>
> whenever it try to enqueue the packet, the skb->len ( range from 2980 - 2977 ) is usually greator than q->max_size ( 2907 )
> hence it drops the packet.
>
> On a different machine with same source code, skb->len never become > 1500 and there the tbf works fine.
>
> Could someone please provide more insight or help where should i look more?
>
> Thanks,
> ~Basit
>
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