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Re: Throughput riddle

From David Christensen <dpchrist@holgerdanske.com>
Newsgroups linux.debian.user
Subject Re: Throughput riddle
Date 2016-03-24 02:50 +0100
Message-ID <rg2zp-3Dt-11@gated-at.bofh.it> (permalink)
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On 03/21/2016 09:28 PM, Celejar wrote:
> On Sun, 20 Mar 2016 21:49:43 -0700
> David Christensen <dpchrist@holgerdanske.com> wrote:
>> 4.  The laptop TX bytes (1.2 GiB) and NAS RX bytes (731.5 MiB) do not
>> correlate well.
>
> Why would [laptop TX bytes and NAS RX bytes] match?

You want to devise experiments that isolate and measure parameters for 
which you have a hypothesis.  My hypothesis was the laptop TX bytes 
should match NAS RX bytes.


The data did not match my hypothesis, so the next step is to try to 
figure out why.


>> 5.  The NAS TX bytes (15.7 MiB) and laptop RX bytes (691.2 MiB) do not
>> correlate well.
>
> Again, why would they match?

As above, but reversed -- NAS TX bytes and laptop RX bytes.


>> Please try another run per my assumptions, above.  Revise and re-post
>> assumptions as necessary.  Post new ifconfig, iwconfig, dmesg, and
>> anything else that looks like a clue.
>
> [Before testing:]
>
> Laptop:
>
> ifconfig
>
> RX packets:26691 errors:0 dropped:98 overruns:0 frame:0

Why were 98 laptop Rx packets were dropped before testing started?


>            TX packets:16051 errors:0 dropped:0 overruns:0 carrier:0
>            collisions:0 txqueuelen:1000
>            RX bytes:30347357 (28.9 MiB)  TX bytes:2245418 (2.1 MiB)
>
> iwconfig
>
>   Link Quality=67/70  Signal level=-43 dBm
>            Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
>            Tx excessive retries:3577  Invalid misc:417   Missed beacon:0

What does laptop WiFi Tx excessive retries mean?  Why were there 3577 
before testing started?


What does laptop WiFi Tx Invalid misc mean?  Why were there 417 before 
testing started?


>
> Router (wlan0):
>
> RX packets:26691 errors:0 dropped:98 overruns:0 frame:0

Why were 98 router WiFi RX packets dropped before testing started?


>            TX packets:16051 errors:0 dropped:0 overruns:0 carrier:0
>            collisions:0 txqueuelen:1000
>            RX bytes:30347357 (28.9 MiB)  TX bytes:2245418 (2.1 MiB)
>
> Router (eth0):
>
> RX packets:1612778 errors:0 dropped:0 overruns:4594 frame:0

Why were 4594 router wired Rx packets overrun?


>            TX packets:1732474 errors:0 dropped:0 overruns:0 carrier:0
>            collisions:0 txqueuelen:1000
>            RX bytes:439536079 (419.1 MiB)  TX bytes:1175937292 (1.0 GiB)
>            Interrupt:4
> 	
> NAS:
>
> RX packets:552082 errors:0 dropped:36 overruns:0 frame:0

Why were 36 NAS RX packets dropped?


>            TX packets:252654 errors:0 dropped:0 overruns:0 carrier:0
>            collisions:0 txqueuelen:1000
>            RX bytes:823241120 (785.1 MiB)  TX bytes:18133067 (17.2 MiB)
>            Interrupt:87
>
>

All of the above non-zero error statistics indicate problems that need 
to be figured out.


> iperf:
>
> laptop -> NAS: 14.8/20.6/24.2
> NAS -> laptop: 53.9/65.6/67.3
>
> Hm, I never realized this - I'm getting 2-4 times the throughput when
> reversing the direction!
>
> laptop -> router: 8.74/10.2/11.4
> router -> laptop: 53.4/56.2/57.1
>
> Wow, 5-8 times the throughput when reversing! Thanks for the suggestion
> to reverse the tests - I really should have tried that on my own.
>
> Any idea what this means?

The iperf numbers indicate that the router is having a hard time 
receiving from the laptop.  This could be due to a problem with the 
laptop transmitter, the router receiver, or both.


Double-check whatever settings you have available for your WiFi 
interfaces in the laptop and in the router.  Document them.


>
> [After testing:]
...

Your statistics have information from at least four (4) iperf runs.  You 
want to isolated each run, and use automation to get consistency/ 
repeatability -- e.g. use the scientific method.


I'd suggest:

1.  Write a script to gather data -- e.g. prints WiFi interface 
parameters, runs ifconfig, runs iwconfig, grep dmesg, etc..

2.  Write a script that sets up and runs one iperf test.

3.  Write a script that calls #1 and saves the output to a file, calls 
#2 and saves the output to a file, calls #1 again and saves the output 
to a file, and then diff's the output of #1 before and #1 after.


Then:

4.  Cold boot everything.

5.  Run script #3.

6.  Repeat #4 and #5 until you get consistent results.

7.  Change one thing and repeat #6, searching for correlation and/or 
causality.


David

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Thread

Throughput riddle Celejar <celejar@gmail.com> - 2016-03-18 17:50 +0100
  Re: Throughput riddle "John L. Ries" <jries@salford-systems.com> - 2016-03-18 19:50 +0100
    Re: Throughput riddle "John L. Ries" <jries@salford-systems.com> - 2016-03-18 20:30 +0100
      Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-18 20:40 +0100
    Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-18 20:40 +0100
  Re: Throughput riddle David Christensen <dpchrist@holgerdanske.com> - 2016-03-19 02:10 +0100
    Re: Throughput riddle Richard Hector <richard@walnut.gen.nz> - 2016-03-19 02:50 +0100
      Re: Throughput riddle David Christensen <dpchrist@holgerdanske.com> - 2016-03-19 03:10 +0100
        Re: Throughput riddle Richard Hector <richard@walnut.gen.nz> - 2016-03-19 03:50 +0100
          Re: Throughput riddle David Christensen <dpchrist@holgerdanske.com> - 2016-03-19 04:50 +0100
          Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-20 14:20 +0100
    Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-20 14:20 +0100
      Re: Throughput riddle David Christensen <dpchrist@holgerdanske.com> - 2016-03-20 17:40 +0100
        Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-20 19:10 +0100
          Re: Throughput riddle David Christensen <dpchrist@holgerdanske.com> - 2016-03-20 21:50 +0100
            Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-21 03:20 +0100
              Re: Throughput riddle David Christensen <dpchrist@holgerdanske.com> - 2016-03-21 06:00 +0100
                Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-22 05:30 +0100
                Re: Throughput riddle David Christensen <dpchrist@holgerdanske.com> - 2016-03-24 02:50 +0100
                Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-24 04:10 +0100
  Re: Throughput riddle arian <debian@semioptimal.net> - 2016-03-20 14:50 +0100
    Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-20 15:50 +0100
      Re: Throughput riddle arian <debian@semioptimal.net> - 2016-03-20 16:30 +0100
        Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-20 18:40 +0100
        Re: Throughput riddle Andrew McGlashan <andrew.mcglashan@affinityvision.com.au> - 2016-03-20 19:50 +0100
  RE: Throughput riddle Bonno Bloksma <b.bloksma@tio.nl> - 2016-03-21 12:50 +0100
    Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-22 05:40 +0100
  Re: Throughput riddle Dan Purgert <dan@djph.net> - 2016-03-21 13:30 +0100
    Re: Throughput riddle Celejar <celejar@gmail.com> - 2016-03-22 05:50 +0100
      Re: Throughput riddle David <david.g_jones@ntlworld.com> - 2016-03-22 11:20 +0100
        RE: Throughput riddle Bonno Bloksma <b.bloksma@tio.nl> - 2016-03-22 13:40 +0100

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