Updating our TCP and socket sysctl values...

Gordon Tetlow gordon at tetlows.org
Sun Mar 20 19:15:22 UTC 2011

On Sat, Mar 19, 2011 at 6:19 PM, Navdeep Parhar <nparhar at gmail.com> wrote:
> I meant 100us (microseconds), sorry.  My point still stands - 10G
> networks have much less one way delay than this.  The worst  I can
> find in the lab right now has around ~30us delay.  A socket rcv
> bufsize of 64K maxes out the link in some casual testing with netperf
> (with autosizing disabled).  256K is already more than what's needed.

Let's look at something much more realistic on the internet. How about
a 100Mbps link with 100ms delay. That's downloading something from
Europe from the US. I do this at work all of the time. The BDP for
such a link is ~1.2MB. This is a pretty common scenario today and it's
not even close to what is reasonably capable (a reliable 1Gbps link
over the same delay distance).

Looking at other operating systems:
Linux (CentOS 5.4):
Read window:
Initial: 87380
Max: 4194304

Write window:
Initial: 16384
Max: 4194304

Solaris 10:
Read window:
Initial: 49152
Max: 1048576

Write window:
Initial: 49152
Max: 1048576

What is the FreeBSD initial setting? Is that sendspace (32k) and
recvspace (64k)? Should we look at changing those too or just discuss
the maximum window sizes?


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