netdev - net_sched: precision problem of TBF/HTB

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Date:	Tue, 16 Jul 2013 12:12:05 +0800
From:	Yang Yingliang <yangyingliang@...wei.com>
To:	Eric Dumazet <edumazet@...gle.com>
CC:	<netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>
Subject: net_sched: precision problem of TBF/HTB

Hi, Eric
Commit 1def9238d4aa2 (net_sched: more precise pkt_len computation) makes more precise transfer bytes by taking account of headers in qdisc_skb_cb(skb)->pkt_len, but this introduces a problem with calculating bandwidth in userland.

When calculating bandwidth in userland, it's not include headers' bytes. From the user's perspective, it's not a correct bandwidth.

Shall we need take account of headers in qdisc_skb_cb(skb)->pkt_len or just skb->len?

Example:
tc qdisc add dev $DEV root handle 1: tbf latency 50ms burst 500kB rate 500mbit mtu 64k

iperf -c host -t 30 -i 10
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   571 MBytes   479 Mbits/sec
[  3] 10.0-20.0 sec   570 MBytes   478 Mbits/sec
[  3] 20.0-30.0 sec   570 MBytes   478 Mbits/sec
[  3]  0.0-30.0 sec  1.67 GBytes   478 Mbits/sec

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