Re: Controlling TCP window size

[Andy Furniss <lists@andyfurniss.entadsl.com>]

John Heffner wrote:
> Andy Furniss wrote:
> 
>>
>> I've been doing some testing of my new wan connection and noticed that 
>> when I specify a window with ip route it still changes after a while.
> 
> 
> Looks like this is occurring in 
> net/ipv4/tcp_input.c:tcp_rcv_space_adjust().
> 
> The problem really is that the window_clamp variable is overloaded. It's 
> used as a kind of cache for rcvbuf -> window conversion, but also as a 
> user-settable bound in window size.  On examination, it looks like this 
> is also broken (in that window size won't increase) if a user does a 
> setsockopt(SO_RCVBUF).  Can we make window_clamp a true clamp?  Then we 
> can get rid of the hack of raising it in tcp_rcv_space_adjust().  I can 
> cook up a patch if interested.
> 
>   -John
> 

Thanks - I did get an answer off list (probably accidently?) to the 
effect that I shouldn't rely on ip route to limit window as it's only a 
hint and would make more sense if I wanted it to start really big.

Playing with r_mem etc is the way to go to hard limit.

Andy.