Re: Throughput riddle
On Wed, 23 Mar 2016 18:48:23 -0700
David Christensen <dpchrist@holgerdanske.com> wrote:
> 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.
My point was that the laptop is transmitting lots of data to
destinations other than the NAS, and the NAS has much less network
activity going on, so why would we expect any correlation between those
two figures?
I think I understand what you mean. You're assuming a cold boot, so
there would be no other traffic. These measurements have actually been
taken from systems that have been up and running for a while.
> >> 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?
This is not from a cold boot, but from a running system.
> > 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
Don't know.
> before testing started?
Again, this is not from a cold boot.
> What does laptop WiFi Tx Invalid misc mean? Why were there 417 before
> testing started?
As above.
> > Router (wlan0):
> >
> > RX packets:26691 errors:0 dropped:98 overruns:0 frame:0
>
> Why were 98 router WiFi RX packets dropped before testing started?
As above.
> > 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?
As above.
> > 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?
As above.
> > 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.
I have been coming to the tentative conclusion that the problem is with
the laptop transmitter. Just now, I got:
laptop -> router: 12.7/13.0/14.4 Mbps
but from an android phone physically located right next to the laptop, I got:
phone -> router: 35.4/40.3/43.9
...
Thanks for the suggestions,
Celejar
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