Odd TCP RFC1323 Behavior

[Chip Marshall]

On 12-Aug-2011, Kevin Oberman <kob6558 at gmail.com> sent:
> Try installing security/openssh-portable from ports and enable
> the HPN patches.
> 
> As it stands today, openssh locks the window size to a tiny
> value. This causes performance over wide area links to be
> simply terrible.
> 
> Take a look at http://fasterdata.es.net/fasterdata/say-no-to-
> scp/ for more information on the issue. As you will see there,
> window scaling is the least of the performance issues with
> openssh.

I've installed OpenSSH with the HPN patch on both the sender and
receiver and repeated my tests, but it doesn't appear to be any
better. As I understand it, if either side of the TCP connection
declines to use RFC1323, the TCP receive window can't get any
larger than 65K, which appears to be the limiting factor here.

Before HPN:
chip at test-client:~> scp test-server:~/testfile ./
testfile                                      100%   10MB 269.5KB/s 00:38    

After HPN:
chip at test-client:~> /usr/local/bin/scp test-server:~/testfile ./
testfile                            100%   10MB 269.5KB/s 448.0KB/s 00:38    

If I go in the other direction, I get better throughput. In this
case, both sides are using RFC1323 window scaling:

Before HPN:
chip at test-server:~$ scp testfile test-client:~/
testfile                            100%   10MB 409.6KB/s 800.0KB/s 00:25    

After HPN:
chip at test-server:~$ scp testfile test-client:~/
testfile                            100%   10MB 445.2KB/s 576.0KB/s 00:23    

-- 
Chip Marshall <chip at 2bithacker.net>
http://weblog.2bithacker.net/          KB1QYW        PGP key ID 43C4819E
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