Re: [Cake] cake flenter results round 1

[Georgios Amanakis <gamanakis@gmail.com>]

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Dear Pete,

I am trying to replicate the unfair behaviour you are seeing with
dual-{src,dst}host, albeit on different hardware and I am getting a fair
distribution. Hardware are Xeon E3-1220Lv2 (router), i3-3110M(Clients). All
running Archlinux, latest cake and patched iproute2-4.14.1, connected with
Gbit ethernet, TSO/GSO/GRO enabled.

Qdisc setup:
----------------
Router:
qdisc cake 8003: dev ens4 root refcnt 2 bandwidth 900Mbit diffserv3
dual-dsthost rtt 100.0ms raw

Client A(kernel default):
qdisc fq_codel 0: dev eno2 root refcnt 2 limit 10240p flows 1024 quantum
1514 target 5.0ms interval 100.0ms memory_limit 32Mb ecn

Client B (kernel default):
qdisc fq_codel 0: dev enp1s0 root refcnt 2 limit 10240p flows 1024 quantum
1514 target 5.0ms interval 100.0ms memory_limit 32Mb ecn
----------------


Cli:
----------------
Router:
netserver &

Client A:
flent tcp_1down -H router

Client B:
flent tcp_12down -H router
----------------


Results:
----------------
Router:
qdisc cake 8003: root refcnt 2 bandwidth 900Mbit diffserv3 dual-dsthost rtt
100.0ms raw
 Sent 7126680117 bytes 4725904 pkt (dropped 10, overlimits 4439745 requeues
0)
 backlog 0b 0p requeues 0
 memory used: 1224872b of 15140Kb
 capacity estimate: 900Mbit
                 Bulk   Best Effort      Voice
  thresh     56250Kbit     900Mbit     225Mbit
  target         5.0ms       5.0ms       5.0ms
  interval     100.0ms     100.0ms     100.0ms
  pk_delay        14us       751us         7us
  av_delay         2us       642us         1us
  sp_delay         1us         1us         1us
  pkts          109948     4601651       14315
  bytes      160183242  6964893773     1618242
  way_inds           0       21009           0
  way_miss         160         188           5
  way_cols           0           0           0
  drops              0          10           0
  marks              0           0           0
  ack_drop           0           0           0
  sp_flows           0           1           1
  bk_flows           1           0           0
  un_flows           0           0           0
  max_len         7570       68130        1022


Client A:
                           avg       median          # data pts
 Ping (ms) ICMP :         0.11         0.08 ms              350
 TCP download   :       443.65       430.38 Mbits/s         301


Client B:
                             avg       median          # data pts
 Ping (ms) ICMP   :         0.09         0.06 ms              350
 TCP download avg :        37.03        35.87 Mbits/s         301
 TCP download sum :       444.35       430.40 Mbits/s         301
 TCP download::1  :        37.00        35.87 Mbits/s         301
 TCP download::10 :        37.01        35.87 Mbits/s         301
 TCP download::11 :        37.02        35.87 Mbits/s         301
 TCP download::12 :        37.00        35.87 Mbits/s         301
 TCP download::2  :        37.03        35.87 Mbits/s         301
 TCP download::3  :        36.99        35.87 Mbits/s         301
 TCP download::4  :        37.03        35.87 Mbits/s         301
 TCP download::5  :        37.07        35.87 Mbits/s         301
 TCP download::6  :        37.00        35.87 Mbits/s         301
 TCP download::7  :        37.12        35.87 Mbits/s         301
 TCP download::8  :        37.05        35.87 Mbits/s         301
 TCP download::9  :        37.03        35.87 Mbits/s         301
----------------

Does this suggest that it is indeed a problem of an underpowered CPU in
your case?

George


On Mon, Nov 27, 2017 at 10:53 AM, Pete Heist <peteheist@gmail.com> wrote:

>
> On Nov 27, 2017, at 3:48 PM, Jonathan Morton <chromatix99@gmail.com>
> wrote:
>
> It's not at all obvious how we'd detect that.  Packets are staying in the
> queue for less time than the codel target, which is exactly what you'd get
> if you weren't saturated at all.
>
> That makes complete sense when you put it that way. Cake has no way of
> knowing why the input rate is lower than expected, even if it’s part of the
> cause.
>
> I don’t think flent can know this either. It can’t easily know the cause
> for its total output to be lower than expected.
>
> All I know is, this is a common problem in deployments, particularly on
> low-end hardware like ER-Xs, that can be tricky for users to figure out.
>
> I don’t even think monitoring CPU in general would work. The CPU could be
> high because it’s doing other calculations, but there’s still enough for
> cake at a low rate, and there’s no need to warn in that case. I’d be
> interested in any ideas on how to know this is happening in the system as a
> whole. So far, there are just various clues that one needs to piece
> together (no or few drops or marks, less total throughput that expected,
> high cpu without other external usage, etc). Then it needs to be proven
> with a test.
>
> Anyway thanks, your clue was what I needed! I need to remember to review
> the qdisc stats when something unexpected happens.
>
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>
>

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