Re: [Cake] WAN ingress rate with concurrent downloads

Re: [Cake] WAN ingress rate with concurrent downloads

[George Amanakis]

Dear All,

regarding the issue about WAN ingress rate with many concurrent TCP downloads, it seems that all the excess ingress rate on the WAN interface are TCP retransmission packets (Wireshark). After the latest commit 78ff814 in cobalt, ping times while using TCP BitTorrent improved from ~1000ms to ~300ms (concurrent connections 55). If I reduce the concurrent connections to 30 I get ping times lower than 70ms.

Best regards,
George

Re: [Cake] WAN ingress rate with concurrent downloads

[Benjamin Cronce]

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It sounds like the sender has a buffer bloat issue. I see the same thing
with bittorrent and tcp. If I rate limit my 150mb connection to 100mb, I
will see about 30-40mb of retransmissions, for a total of ~135mb of
ingress. Even though I limit only to 100mb.

If I trace route the offending senders, I always see a 3000ms+ ping 1-2
hops before I reach them.

Tcp treats the buffer bloat as packet loss, flooding the receiver.

On Dec 9, 2016 1:20 PM, "George Amanakis" <g_amanakis@yahoo.com> wrote:

> Dear All,
>
> regarding the issue about WAN ingress rate with many concurrent TCP
> downloads, it seems that all the excess ingress rate on the WAN interface
> are TCP retransmission packets (Wireshark). After the latest commit 78ff814
> in cobalt, ping times while using TCP BitTorrent improved from ~1000ms to
> ~300ms (concurrent connections 55). If I reduce the concurrent connections
> to 30 I get ping times lower than 70ms.
>
> Best regards,
> George
> _______________________________________________
> Cake mailing list
> Cake@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cake
>

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Re: [Cake] WAN ingress rate with concurrent downloads

[Georgios Amanakis]

Dear All,

I think Sebastian's theory has a weak point. 

> Again I believe you just show bit-torrent misbehaving ...

I can easily reproduce this behaviour if one LAN-host downloads
multiple files using TCP (e.g. 2 or more kernels simultaneously from ht
tp://www.kernel.org). 

> For me this looks like bwmon accounts the incoming packets before
> cake sees and drops them ...

If only one download takes place then the bandwidth bmon reports on
WAN-ingress is the same as the limit set in cake. I don't think that
bmon accounts the incoming packets before cake sees them. Furthermore,
Wireshark reports that all bittorrent traffic in my case are TCP
packets, and reports the same bandwidth usage as bmon on WAN-ingress. 

The only way I have found that WAN-ingress limit is obeyed, is using
act_police with the in-kernel bandwidth estimator (i.e. tc filter add
dev enp0s13 parent ffff: protocol all estimator 10msec 80msec u32 match
u32 0 0 police avrate 3300kbit drop flowid :1). But then there is an
discrepancy between WAN-ingress and LAN-egress (i.e. WAN-ingress is at
~400kbytes/s and LAN-egress on the host running bittorrent is
~220kbytes/s). Unfortunately I cannot see the bandwidth my cable-modem
syncs at (I searched the web-interface but did not find it; it is a
Comcast-provided Arris TG1682G).

Noah, could you try and see what happens if instead of bittorrent a
LAN-host downloads multiple files using TCP?

Thank you all for your feedback,
George

Re: [Cake] WAN ingress rate with concurrent downloads

[Sebastian Moeller]

Hi Georgios,


> On Oct 30, 2016, at 17:43, Georgios Amanakis <g_amanakis@yahoo.com> wrote:
> 
> Dear All,
> 
> I think Sebastian's theory has a weak point. 

	Oh, I do not claim to be an expert on these matters, so would cherish input from others, but I do think my hypothesis is not to be dismissed completely (see below).

> 
>>  Again I believe you just show bit-torrent misbehaving ...
> 
> I can easily reproduce this behaviour if one LAN-host downloads
> multiple files using TCP (e.g. 2 or more kernels simultaneously from ht
> tp://www.kernel.org). 
> 
>> For me this looks like bwmon accounts the incoming packets before
>> cake sees and drops them ...
> 
> If only one download takes place then the bandwidth bmon reports on
> WAN-ingress is the same as the limit set in cake. I don't think that
> bmon accounts the incoming packets before cake sees them.

	That could be true, but also should be testable. According to http://bwmon.sourceforge.net bwmon reads /proc/net/dev to get its estimates, so “cat /proc/net/dev” should show you what is in there:

Directly after reboot:
root@turris:~# cat /proc/net/dev
Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
  gre0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
 wlan0:  526875    2287    0    0    0     0          0         0   693742    2001    0    0    0     0       0          0
  sit0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
gretap0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
    lo:    2175      26    0    0    0     0          0         0     2175      26    0    0    0     0       0          0
ifb4eth1:  740189    2097    0    0    0     0          0         0   740189    2097    0    0    0     0       0          0
  eth0:       0       0    0    0    0     0          0         0    17543      84    0    0    0     0       0          0
  eth1:  752467    2167    0    0    0     0          0         0   541001    2390    0    0    0     0       0          0
  eth2:       0       0    0    0    0     0          0         0    17497      83    0    0    0     0       0          0
ip6tnl0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
 wlan1:       0       0    0    0    0     0          0         0    17875      76    0    0    0     0       0          0
br-lan:  494863    2288    0    0    0     0          0         0   627972    1881    0    0    0     0       0          0
  ifb0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
 teql0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
  ifb1:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0


After a dslreports speedtest with 16/16 streams:
root@turris:~# cat /proc/net/dev
Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
  gre0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
 wlan0: 20160809   37095    0    0    0     0          0         0 48570975   44819    0    0    0     0       0          0
  sit0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
gretap0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
    lo:    2453      28    0    0    0     0          0         0     2453      28    0    0    0     0       0          0
ifb4eth1: 47764269   44632    0    0    0     0          0         0 47764269   44632    0    0    0     0       0          0
  eth0:       0       0    0    0    0     0          0         0    20435     100    0    0    0     0       0          0
  eth1: 48135827   45333    0    0    0     0          0         0 19357920   36538    0    0    0     0       0          0
  eth2:       0       0    0    0    0     0          0         0    20389      99    0    0    0     0       0          0
ip6tnl0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
 wlan1:       0       0    0    0    0     0          0         0    21047      92    0    0    0     0       0          0
br-lan: 19641491   37097    0    0    0     0          0         0 47617521   44254    0    0    0     0       0          0
  ifb0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
 teql0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
  ifb1:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
root@turris:~# 


Please notice how eth1 reports initially 2167-2097 = 70 packets more than ifb4eth1 (the shapers ingress qdisc is attached to the IFB as linux does not allow shapers on ingress without the ifb trick, policers however can directly act in ingress). After the test we see 45333-44632 = 701 Packets more on eth1 than ifb4eth1. I take this as supporting evidence for my hypothesis...

> Furthermore,
> Wireshark reports that all bittorrent traffic in my case are TCP
> packets, and reports the same bandwidth usage as bmon on WAN-ingress. 

	Well, if both look at the raw enp0s13 interface I would expect both of them to report the traffic before packets can be dropped.


> 
> The only way I have found that WAN-ingress limit is obeyed, is using
> act_police with the in-kernel bandwidth estimator (i.e. tc filter add
> dev enp0s13 parent ffff: protocol all estimator 10msec 80msec u32 match
> u32 0 0 police avrate 3300kbit drop flowid :1).

	As stated above, I believe I recall that policers can directly act on ingress and hence affect the number of packets reported for that interface...

> But then there is an
> discrepancy between WAN-ingress and LAN-egress (i.e. WAN-ingress is at
> ~400kbytes/s and LAN-egress on the host running bittorrent is
> ~220kbytes/s). Unfortunately I cannot see the bandwidth my cable-modem
> syncs at (I searched the web-interface but did not find it; it is a
> Comcast-provided Arris TG1682G).

	With DOCSIS systems there is no clear and easy way to get hod on the relevant numbers (which would be the numbers your ISP plugged into the CMTS shaper and information about potentially allowed bursts).

> 
> Noah, could you try and see what happens if instead of bittorrent a
> LAN-host downloads multiple files using TCP?

	I would also be interested in the outcome of that test, please keep posting to the list.

Best Regards
	Sebastian

> 
> Thank you all for your feedback,
> George
> _______________________________________________
> Cake mailing list
> Cake@lists.bufferbloat.net
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[Cake] WAN ingress rate with concurrent downloads

[G. Amanakis]

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Hi All,

I noticed that the ingress rate on the WAN interface as reported by bmon or bwm-ng does not reflect the setting in cake (on ifb ingress or on LAN egress) when one of the hosts is using bittorrent or when there are more than 3 concurrent downloads on a 3300kbit/s bandwidth (router behind cable modem). With 1-2 concurrent downloads (i.e. connections) the ingress rate reported on WAN matches the limit set in cake. The same thing happens with HTB, TBF, or the police action. Any ideas why?

Greetings,
George

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Re: [Cake] WAN ingress rate with concurrent downloads

[G. Amanakis]

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I mean that the ingress limit on WAN (or egress limit on LAN) seems to be ignored, and the rate bmon and bwm-ng report is the maximum achievable. I.e. on 450kbyte/s ingress with the limit set at 400kbyte/s, when bittorrent is in use bmon reports 450kbyte/s after 10-20 seconds.

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Re: [Cake] WAN ingress rate with concurrent downloads

[Sebastian Moeller]

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Could you set the ingress shaper to 50% of you true ingress rate and try again, please?
Also could you post the results of 'tc -d qdisc' with your current settings and with the 50% settings (I will probably ask for more data...)? And finally I believe you are on an ADSL link, what are the sync rates reported by the modem, and which ISP are you with (I ask, as some ISPs actually employ a shaper at their BRAS, so the modem sync rate might not be the actual bottleneck bandwidth). That said, with wrong shaper settings I would rather expect increased latency under load, but not bandwidth violations.

Best Regards
        Sebastian

On October 27, 2016 2:16:06 AM GMT+02:00, "G. Amanakis" <g_amanakis@yahoo.com> wrote:
>I mean that the ingress limit on WAN (or egress limit on LAN) seems to
>be ignored, and the rate bmon and bwm-ng report is the maximum
>achievable. I.e. on 450kbyte/s ingress with the limit set at
>400kbyte/s, when bittorrent is in use bmon reports 450kbyte/s after
>10-20 seconds.
>
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Re: [Cake] WAN ingress rate with concurrent downloads

[Noah Causin]

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I notice this behavior as well.  I believe it is the fact that SQM is 
not the true bottleneck.  Senders continue to increase their transfer 
rate until active queue management on your router causes them to slow down.

If I watch LEDE's built-in realtime traffic graphs, I do see incoming 
rates higher than the set limit.


On 10/27/2016 2:41 AM, Sebastian Moeller wrote:
> Could you set the ingress shaper to 50% of you true ingress rate and 
> try again, please?
> Also could you post the results of 'tc -d qdisc' with your current 
> settings and with the 50% settings (I will probably ask for more 
> data...)? And finally I believe you are on an ADSL link, what are the 
> sync rates reported by the modem, and which ISP are you with (I ask, 
> as some ISPs actually employ a shaper at their BRAS, so the modem sync 
> rate might not be the actual bottleneck bandwidth). That said, with 
> wrong shaper settings I would rather expect increased latency under 
> load, but not bandwidth violations.
>
> Best Regards
> Sebastian
>
> On October 27, 2016 2:16:06 AM GMT+02:00, "G. Amanakis" 
> <g_amanakis@yahoo.com> wrote:
>
>     I mean that the ingress limit on WAN (or egress limit on LAN)
>     seems to be ignored, and the rate bmon and bwm-ng report is the
>     maximum achievable. I.e. on 450kbyte/s ingress with the limit set
>     at 400kbyte/s, when bittorrent is in use bmon reports 450kbyte/s
>     after 10-20 seconds.
>
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Re: [Cake] WAN ingress rate with concurrent downloads

[Georgios Amanakis]

Hi Sebastian,

the ISP is Comcast in MD, USA, residential connection. It is a cable
connection (i.e. the WAN port on the modem is a coaxial one) and not a
DSL one. Maximum ingress rate is ~450kbytes/s which is what the modem
syncs at. By using "test_WAN_dual-isolate__piece_of_cake.qos", "tc -d
qdisc show" reports (enp0s13 is WAN, enp0s14 is LAN):
-------8<--------
qdisc noqueue 0: dev lo root refcnt 2 
qdisc fq_codel 0: dev enp0s14 root refcnt 2 limit 10240p flows 1024 		
quantum 1514 target 5.0ms interval 100.0ms ecn 
qdisc cake 8002: dev enp0s13 root refcnt 2 bandwidth 900Kbit besteffort
		dual-srchost nat rtt 100.0ms raw 
qdisc ingress ffff: dev enp0s13 parent ffff:fff1 ---------------- 
qdisc fq_codel 0: dev ifb0 root refcnt 2 limit 10240p flows 1024 		
quantum 1514 target 5.0ms interval 100.0ms ecn 
qdisc cake 8003: dev ifb4enp0s13 root refcnt 2 bandwidth 3300Kbit 		
besteffort dual-dsthost nat rtt 100.0ms raw 
-------8<--------

If one of the hosts on LAN is running bittorrent, bmon on the gateway
reports:
		RX bps 		RXpps	TX bps		TXpps
enp0s14		23.55KiB	303	402.87KiB	322
enp0s13		457.26KiB	369	25.04KiB	307


Setting the ingress rate at 1900kbps (instead of 3300kbps as above),
"tc -d qdisc show" reports:
-------8<--------
qdisc noqueue 0: dev lo root refcnt 2 
qdisc fq_codel 0: dev enp0s14 root refcnt 2 limit 10240p flows 1024 		
quantum 1514 target 5.0ms interval 100.0ms ecn 
qdisc cake 8008: dev enp0s13 root refcnt 2 bandwidth 900Kbit besteffort
		dual-srchost nat rtt 100.0ms raw 
qdisc ingress ffff: dev enp0s13 parent ffff:fff1 ---------------- 
qdisc fq_codel 0: dev ifb0 root refcnt 2 limit 10240p flows 1024 		
quantum 1514 target 5.0ms interval 100.0ms ecn 
qdisc cake 8009: dev ifb4enp0s13 root refcnt 2 bandwidth 1900Kbit 		
besteffort dual-dsthost nat rtt 100.0ms raw 
-------8<--------

Using bittorrent, bmon on the gateway reports:
		RX bps 		RXpps	TX bps		
TXpps
enp0s14		19.25KiB	219	232.51KiB	184
enp0s13		393.36KiB	304	20.25KiB	220

In both cases the ingress rate limit on the WAN interface (enp0s13) is
not obeyed. I verified these data by using tcpdump and doing an IO-
Graph with wireshark.

Looking forward to your feedback,
George

Re: [Cake] WAN ingress rate with concurrent downloads

[Sebastian Moeller]

Hi Georgios,


> On Oct 28, 2016, at 03:34, Georgios Amanakis <g_amanakis@yahoo.com> wrote:
> 
> Hi Sebastian,
> 
> the ISP is Comcast in MD, USA, residential connection. It is a cable
> connection (i.e. the WAN port on the modem is a coaxial one) and not a
> DSL one.

	Interesting, from the bandwidth I had assumed ADSL ;)

> Maximum ingress rate is ~450kbytes/s which is what the modem
> syncs at.

MMh typically sync-rates are soecified in Kbps or 10^3 Bits per second, not KiloBytes and certainly not 2^10 Bytes; could you clarify what exactly your modem reports and what the best numbers you get from speedtests (like dslreoorts.com) without active AQM/cake/htb, please?


> By using "test_WAN_dual-isolate__piece_of_cake.qos", "tc -d
> qdisc show" reports (enp0s13 is WAN, enp0s14 is LAN):
> -------8<--------
> qdisc noqueue 0: dev lo root refcnt 2 
> qdisc fq_codel 0: dev enp0s14 root refcnt 2 limit 10240p flows 1024 		
> quantum 1514 target 5.0ms interval 100.0ms ecn 
> qdisc cake 8002: dev enp0s13 root refcnt 2 bandwidth 900Kbit besteffort
> 		dual-srchost nat rtt 100.0ms raw 
> qdisc ingress ffff: dev enp0s13 parent ffff:fff1 ---------------- 
> qdisc fq_codel 0: dev ifb0 root refcnt 2 limit 10240p flows 1024 		
> quantum 1514 target 5.0ms interval 100.0ms ecn 
> qdisc cake 8003: dev ifb4enp0s13 root refcnt 2 bandwidth 3300Kbit 		
> besteffort dual-dsthost nat rtt 100.0ms raw 
> -------8<--------
> 
> If one of the hosts on LAN is running bittorrent, bmon on the gateway
> reports:
> 			RX bps 		RXpps	TX bps		TXpps
> enp0s14		23.55KiB		303		402.87KiB	322
> enp0s13		457.26KiB	369		25.04KiB		307
> 

Okay so:
900Kbps = 900 * 1000 / (8 * 1024) = 109.86328125 KiB
3300Kbps = 3300 * 1000 / (8 * 1024) = 402.83203125 KiB

So it looks like enp0s14-TX actually shows the specified internet-download rate, (internet upload is not maxed out)



> 
> Setting the ingress rate at 1900kbps (instead of 3300kbps as above),
> "tc -d qdisc show" reports:
> -------8<--------
> qdisc noqueue 0: dev lo root refcnt 2 
> qdisc fq_codel 0: dev enp0s14 root refcnt 2 limit 10240p flows 1024 		
> quantum 1514 target 5.0ms interval 100.0ms ecn 
> qdisc cake 8008: dev enp0s13 root refcnt 2 bandwidth 900Kbit besteffort
> 		dual-srchost nat rtt 100.0ms raw 
> qdisc ingress ffff: dev enp0s13 parent ffff:fff1 ---------------- 
> qdisc fq_codel 0: dev ifb0 root refcnt 2 limit 10240p flows 1024 		
> quantum 1514 target 5.0ms interval 100.0ms ecn 
> qdisc cake 8009: dev ifb4enp0s13 root refcnt 2 bandwidth 1900Kbit 		
> besteffort dual-dsthost nat rtt 100.0ms raw 
> -------8<--------
> 
> Using bittorrent, bmon on the gateway reports:
> 		RX bps 		RXpps	TX bps		
> TXpps
> enp0s14		19.25KiB	219	232.51KiB	184
> enp0s13		393.36KiB	304	20.25KiB	220
> 

Okay so:
900Kbps = 900 * 1000 / (8 * 1024) = 109.86328125 KiB
3300Kbps = 1900 * 1000 / (8 * 1024) = 231.93359375 KiB

And again enp0s14-TX shows the specified internet-download rate, (internet upload is not maxed out)

For me this looks like bwmon accounts the incoming packets before cake sees and drops them (the enp0s14-TX shows that cake does only transmit the specified rate into the LAN, so cake does its job)). Then the fact that enp0s13 (btw these new interface names have not yet grown on me, yuck) sees more incoming packets simply means that the bit torrent peers are an unruly bunch and do not react nicely to cakes drops and marks (are the packets ECN labeled?). Bit-torrent, when using its µTP protocol tries to use increasing delay as signal to throttle, but cake removes that latency increase under load, which mjight make the torrent peers not scale back their TX rates based on a wrong believe that there is more link capacity available. Not that anybody asks me, but I believe µTP actively is a bad thing and all torrent peers shoud default to TCP instead of µTP?UDP, but I digress.


> In both cases the ingress rate limit on the WAN interface (enp0s13) is
> not obeyed. I verified these data by using tcpdump and doing an IO-
> Graph with wireshark.

	Well that is true in that cake does not run a lower rate on the ethernet interface, but what it does happens after packets are passed from the NIC to the OS. Again I believe you just show bit-torrent misbehaving, a nice illustration why we can’t have nice things, erm why non-latency-inducing shapers, like cake and HTB+fq_codel have a hard time ruling in bit-torrent… BTW, can you see from your packet captures how long a typical torrent-flow actually exists and is active? So are these say a few dozend long-term flows or a swarm of dozens of flows that come and go on a seconds time-frame?

Best Regards
	Sebastian

> 
> Looking forward to your feedback,

P.S.: I am just an amateur in these matters, so other’s on the cake list will surely be able to give better advice. So @experts, please holler if my theory above does not make sense...


> George
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