Re: NetBSD TCP Congestion Control Configuration

[David Laight <david%l8s.co.uk@localhost>]

On Wed, Jan 07, 2009 at 09:33:39AM -0500, Steven M. Bellovin wrote:
> 
> Remember that slow start is much older than NetBSD; I don't think
> you'll find any versions of the code that don't have it.  And, since
> turning it off is regarded as a very unfriendly thing to do on the
> Internet, I suspect that no one saw any reason to add such a sysctl.
> Your need is legitimate, but I think you'll have to modify the code
> yourself.

OTOH I've recently seen bad interactions between 'slow start' and
'delayed acks' on fast local connections (with Nagle disabled).

I think that 'slow start' is restarted every time there are no
unacked bytes - ie almost always!

The 'delayed acks' seems to delay for ~30ms (this was a Linux system)
instead of sending an ack every other data packet.

The program is trying to send a short TCP data packet about every 2ms.
After 4 packets without an ack it stops sending :-( even when it
has more than 1500 bytes bufferred!

I found some stuff that implied similar things had been seen when abc
(appropriate byte counting) was enabled - but that had no effect.

It did seem to me that some of the changes made for ftp/web over
large latency links have f**ck*d short latence links that are not
carrying either bulk data or command-response traffic.

        David

-- 
David Laight: david%l8s.co.uk@localhost