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On 03/12/16 19:13, Steinar H. Gunderson wrote:<br>
> On Sat, Dec 03, 2016 at 08:03:50AM -0500, Neal Cardwell wrote:<br>
<br>
>>> I have one thing that I _wonder_ if could be BBR's
fault: I run<br>
>>> backup over SSH. (That would be tar + gzip + ssh.) The
first full<br>
>>> backup after I rolled out BBR on the server (the one
sending the<br>
>>> data) suddenly was very slow (~50 Mbit/sec); there was
plenty of<br>
>>> free I/O, and neither tar nor gzip (well, pigz) used a
full core.<br>
>>> My only remaining explanation would be that somehow,
BBR didn't<br>
>>> deal well with the irregular stream of data coming from
tar. (A<br>
>>> wget between the same machines at the same time gave
6-700<br>
>>> Mbit/sec.)<br>
<br>
>> Thanks for the report, Steinar. This is the first report
we've had<br>
>> like this, but it would be interesting to find out what's
going<br>
>> on.<br>
>><br>
>> Even if you don't have time to apply the patches Eric
mentions, it<br>
>> would be hugely useful if the next time you have a slow
transfer<br>
>> like that you could post a link to a tcpdump packet capture<br>
>> (headers only is best, say -s 120). Ideally the trace would<br>
>> capture a whole connection, so we can see the wscale on the
SYN<br>
>> exchange.<br>
><br>
> I tried reproducing it now. I can't get as far down as 50
Mbit/sec,<br>
> but it stopped around 100 Mbit/sec, still without any clear<br>
> bottlenecks. cubic was just as bad, though.<br>
><br>
> I've taken two tcpdumps as requested; I can't reboot this
server<br>
> easily right now, unfortunately. They are:<br>
><br>
> <a class="moz-txt-link-freetext" href="http://storage.sesse.net/bbr.pcap">http://storage.sesse.net/bbr.pcap</a> -- ssh+tar+gnupg<br>
> <a class="moz-txt-link-freetext" href="http://storage.sesse.net/bbr2.pcap">http://storage.sesse.net/bbr2.pcap</a> -- wget between same hosts<br>
><br>
> /* Steinar */<br>
<br>
Since no-one's explicitly mentioned this: be aware that SSH is known
for doing application-level windowing, limiting performance.<br>
<br>
E.g. see <a class="moz-txt-link-freetext" href="https://www.psc.edu/index.php/hpn-ssh/638">https://www.psc.edu/index.php/hpn-ssh/638</a><br>
<br>
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