From: Ding Tianhong <dingtianhong@huawei.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>,
Eric Dumazet <edumazet@google.com>, <netdev@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: net_sched: precision problem of TBF/HTB
Date: Wed, 17 Jul 2013 09:41:03 +0800 [thread overview]
Message-ID: <51E5F62F.8080906@huawei.com> (raw)
In-Reply-To: <1373950201.10804.103.camel@edumazet-glaptop>
On 2013/7/16 12:50, Eric Dumazet wrote:
> On Tue, 2013-07-16 at 12:12 +0800, Yang Yingliang wrote:
>> 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.
>>
> This changed nothing to 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?
>>
> These values are not accessible from userland, unless you capture
> packets with a sniffer (tcpdump or something like that)
>
>> 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
>
>
> iperf only measures the amount of payload, and probably do not care of
> headers.
>
> You cannot accurately measure bandwidth from userland, unless making
> assumptions (or getting them from the stack) on header sizes (IP + TCP),
> MSS value, and retransmits.
>
>
ok, for the further, can you give me some advise for how calculate the bandwidth for net link.
for example,what kind of tools is better.
>
> --
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>
next prev parent reply other threads:[~2013-07-17 1:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-16 4:12 net_sched: precision problem of TBF/HTB Yang Yingliang
2013-07-16 4:50 ` Eric Dumazet
2013-07-17 1:41 ` Ding Tianhong [this message]
2013-07-17 3:18 ` John Fastabend
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