[Make-wifi-fast] Flent results for point-to-point Wi-Fi on LEDE/OM2P-HS available

Toke Høiland-Jørgensen toke at toke.dk
Wed Feb 1 09:53:20 EST 2017

Aaron Wood <woody77 at gmail.com> writes:

>  - Yeah, as you note Flent has a batch facility. Did you not use this
>    simply because you couldn't find it, or was there some other reason?
>    Would love some feedback on what I can do to make that more useful to
>    people... While I have no doubt that your 'flenter.py' works, wrapping
>    a wrapper in this sense makes me cringe a little bit ;)
> Wait, what?  It does?  (I've been using wrapper scripts as well)

Yes, but as you can tell it hasn't seen much usage outside of my own.
Please do try it out and let me know what you think :)

>  - Flent also has a metadata gathering feature where you can get lots of
>    stats from both your qdisc-based bottlenecks, and your WiFi links.
> Again, it does?  Neat!  (I try to bury data into the tag for the
> run...)

Yes. I have still not come up with a good way to use the metadata
afterwards (other than viewing it in the GUI; you can add columns to the
open files view with arbitrary metadata info). Filtering on it, and
adding it to the plots as annotations would probably be useful, but not
sure how to do the API.

Also, the --test-parameter option was originally intended to just be a
way to add arbitrary key/val pairs to the metadata. Every option you
specify that way will be saved in the data file. It has since been
co-opted by some other features, so that some keys will modify the test
behaviour; see the man page for those :)

>  Question 5: For TCP you can't get packet loss from user space; you'll
>  need packet captures for that. So no way to get it from Flent either.
>  You can, however, get average throughput. Look at the box plots; if you
>  run multiple iterations of the same test, you can plot several data
>  files in a single box_combine plot, to get error bars. `flent
>  file.flent.gz -f summary` (which is the default if you don't specify a
>  plot) will get you averages per data series; or you can extract it from
>  the metadata.
> You don't get packet loss, per se, but you can periodically poll the
> TCP_INFO struct via getsockopt() and get the retransmission count
> (which more or less gives you the packet loss rate). (which is what
> iperf3 does to gather stats like it's view of rtt, retransmits, etc).

Yeah, I do believe you can make netperf output that at the end of the
test as well; but Flent currently does not support collecting that.

There's some work underway, also, to poll 'ss' for socket statistics
during the test, so we can get insight into the TCP state machine...


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