On 2015/03/29 14:45, Tinker wrote:
> On 2015-03-29 13:50, Stuart Henderson wrote:
> >On 2015-03-29, Tinker <[email protected]> wrote:
> >>How do I make TCP stack's initial window 10-50KB, so that I can burst
> >>that amount of data without any interference from the TCP slow-start/RFC
> >>3390 anti-congestion whatsoever?
> >
> >OpenBSD already starts with 14600, see around line 3140 in tcp_input.c
> >if you'd like to experiment.
>
> Stuart,
>
> Thank you a lot for your response.
>
> Wait, what line exactly at
> http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sys/netinet/tcp_input.c?annotate=1.287
> is it that sets the initial window size?
>
> (3145 and 3148 seem to refer to that it's already set.. and 3130-3142 too?)
>
>
> And, could I conveniently set this to 50KB via some sysctl setting?
>
> (It seems to me that the mssdflt is used as step size when the
> anticongestion increases and decreases the window size, so I guess just
> increasing it by a multiple of 10 would be a very bad idea.)
>
> Thanks!
> Tinker
>
By default tcp_do_rfc3390=2, so the usual case is this:
1.252 claudio 3143: } else if (tcp_do_rfc3390 == 2) {
3144: /* increase initial window */
3145: tp->snd_cwnd = ulmin(10 * mss, ulmax(2
* mss, 14600));
There is no existing sysctl to allow fine tuning, just the "IW4, max 4380"
and "IW10, max 14600" switch of net.inet.tcp.rfc3390. But you could easily
locally extend that variable if you want to experiment with changing the
multiplier and max value (or something else).
