[Bloat] I am unable to pinpoint the source of bufferbloat

[Dave Taht]

On Sat, Feb 9, 2013 at 2:06 PM, Forums1000 <forums1000 at gmail.com> wrote:

> Excellent information. So an AQM-algorithm will sort things on the OS
> level of the router and should make things considerably better. However,
> from reading around on the matter, it seems drivers for the network device
> and the hardware itself also contain buffers. Since, Dave (and respect for
> that) is developing CeroWRT, is there anything that can be done about that?
> Do we have any idea on how severe the buffering in drivers and hardware is?
>
>
In linux, it's got a lot better in the past 2 years. Work continues.

I have some data on OSX now, and some on windows, but not a lot.

In APs, routers, and switches, it's not looking very good.


However I note that the second biggest place we see the issue is on the
edge home gateways, dslams, cable head-ends, and many of those use software
rate limiting, which generally has 1 buffer or less native to it, and the
underlying buffering doesn't matter.

(then on top of the software rate limiters are big fat dumb drop tails
queues. currently. sigh)




> A little test I just performed using Windows XP now, indeed shows that
> Netalyzr is showing me a worst case scenario:
>
>
Meh. Try something with window scaling. Or, try a netanalyzer test from
some other machine at the same time you do this one.


> - a continuous ping (1 ping per second) between 2 routers under my control
> has an RTT of 20ms (give or take). The remote router I'm pinging sits
> pretty much idle and has nothing better to do than answering the ping.
> - uploading a large file to Google drive (thereby saturating my uplink
> bandwidth) adds +-10ms of additional latency.
>

I think this is an invalid assumption without actually measuring your
transfer rate to the the gdrive. It would not surprise me if their TCP was
pretty sensitive to latency swings, however, they are very on top of the
bufferbloat issue.

Wouldn't mind a packet capture of that upload while doing the above test.



> Sure it varies a bit between 20 and 30ms and goes to 35ms or even 40ms
> regularly. Moreover, every now and then I get a spike to 70-80ms but that
> spike never lasts more than 3 pings.
>
> All in all considerably lower bloat than the 550ms Netalyzr is indicating.
> In order to mimic the worst case scenario, I'd have to transfer using UDP
> then?
>

Just run a more modern OS....


>
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-- 
Dave Täht

Fixing bufferbloat with cerowrt:
http://www.teklibre.com/cerowrt/subscribe.html
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