* net_sched: precision problem of TBF/HTB
@ 2013-07-16 4:12 Yang Yingliang
2013-07-16 4:50 ` Eric Dumazet
0 siblings, 1 reply; 4+ messages in thread
From: Yang Yingliang @ 2013-07-16 4:12 UTC (permalink / raw)
To: Eric Dumazet; +Cc: netdev, David S. Miller
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: net_sched: precision problem of TBF/HTB
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
0 siblings, 1 reply; 4+ messages in thread
From: Eric Dumazet @ 2013-07-16 4:50 UTC (permalink / raw)
To: Yang Yingliang; +Cc: Eric Dumazet, netdev, David S. Miller
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.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: net_sched: precision problem of TBF/HTB
2013-07-16 4:50 ` Eric Dumazet
@ 2013-07-17 1:41 ` Ding Tianhong
2013-07-17 3:18 ` John Fastabend
0 siblings, 1 reply; 4+ messages in thread
From: Ding Tianhong @ 2013-07-17 1:41 UTC (permalink / raw)
To: Eric Dumazet; +Cc: Yang Yingliang, Eric Dumazet, netdev, David S. Miller
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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>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: net_sched: precision problem of TBF/HTB
2013-07-17 1:41 ` Ding Tianhong
@ 2013-07-17 3:18 ` John Fastabend
0 siblings, 0 replies; 4+ messages in thread
From: John Fastabend @ 2013-07-17 3:18 UTC (permalink / raw)
To: Ding Tianhong
Cc: Eric Dumazet, Yang Yingliang, Eric Dumazet, netdev, David S. Miller
On 07/16/2013 06:41 PM, Ding Tianhong wrote:
> 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.
>
>>
Vendor specific but it looks reasonably common to count tx and rx bytes
in ethtool stats. Take a few samples with 'ethtool -S' and do the
math. This will give you what the driver/hardware actually xmits and
receives.
.John
--
John Fastabend Intel Corporation
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2013-07-17 3:19 UTC | newest]
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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
2013-07-17 3:18 ` John Fastabend
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