svn commit: r232345 - user/andre/tcp_workqueue/sys/netinet

[Ivan Voras]

On 1 March 2012 18:53, Andre Oppermann <andre at freebsd.org> wrote:

> I'm a bit wary of abuse by non-clueful enough people who think bigger
> must be better.  There was a recent discussion to this effect on TCPM.
> Also there were reports of congestion collapse in some networks, due
> to some other issues.  I've even seen botched windows servers that
> respond with an icwnd of 64K.
>
> Hence I'd rather not have it open to anyone to fumble with this important
> parameter.  The (negative) effects are not directly visible to a normal
> admin.

AFAIK the whole idea about increasing the initial window was started
in Google; there are some blog posts from their engineers and at least
one paper (http://code.google.com/speed/articles/tcp_initcwnd_paper.pdf).
The reason why they have been able to experiment with it is that it's
so easy to change in Linux:

" the initial congestion window is configured using the intitcwnd
option in the ip route command. "

So, by not having this as tunable, that opportunity was missed by
someone who uses FreeBSD (Yahoo?). Less power to tinker results in
less power to do some innovation.

Even more, the quote I've pasted from the paper suggests it's a
per-route setting in Linux.