Re: hpn_buffer_size

[Chuck Swiger <cswiger%mac.com@localhost>]

On Apr 27, 2012, at 11:43 AM, Petar Bogdanovic wrote:
>> You need to increase the TCP window size to take significant advantage
>> of the SSH HPN changes.  Take a look at the following sysctls:
>> 
>> kern.sbmax
>> net.inet.tcp.rfc1323
>> net.inet.tcp.recvbuf_max
>> net.inet.tcp.sendbuf_max
>> net.inet.tcp.recvspace
>> net.inet.tcp.sendspace
>> 
>> You'll also need to increase NMBCLUSTERS, unless that has become
>> a sysctl tunable as well...
> 
> Thanks for the hints but I'm not sure I understand the logic behind
> this.  HPNDisabled=no is the default setting, and I'm not running high
> powered n Gigabit-Interfaces so why should a default setting in a rather
> unspectacular environment require any additional tweaking?

The defaults are chosen to be reasonable for a wide range of circumstances, 
without consuming a lot of network buffer memory.  If you have a high-speed 
link and want to improve performance, then the default values are not ideal.  
(Note that these values date back to when 10Mbs ethernet was "fast", so even a 
gigabit link could be improved by tuning....)

> Or in other words: Wouldn't a HPNDisabled=yes default make more sense?

Maybe.  HPN also permits some other things like a null crypto type, which is 
useful when you want to use SSH auth, but you don't care about encrypting the 
data being sent....

Regards,
-- 
-Chuck