tcp_output starving -- is due to mbuf get delay?

Borje Josefsson bj at
Fri Apr 11 09:43:04 PDT 2003

On Fri, 11 Apr 2003 09:32:51 PDT Terry Lambert wrote:

> Borje Josefsson wrote:
> > > A good thing to look at at this point would be:
> > >
> > >       o       Clean boot of FreeBSD target
> > >       o       Run NetBSD against it
> > >       o       Save statistics
> > 
> > What type of statistics do You mean?
> Dropped packets; frags; delayed acks.  The stuff you get from
> "netstat -s" and "netstat -m".
> > > You mean "bandwidth delay product".  Yes, assuming you have packet
> > > loss.  From your description of your setup, packet loss should not
> > > be possible, so we can discount it as a factor.
> > 
> > Of cause packet loss is possible on a nationwide network. If I loose a
> > packet on the (expected) 10 second test (with NetBSD), recovering from
> > that drops performance from 900+ to ~550 Mbps. Thos shows very clearly if
> > I run "netstat 1".
> You are running these tests over .se's nationwide network?

One of them, I'm using GigaSunet, the nationwide network for the 
universities in Sweden. 10 Gbps to 22 cities, connecting 35 universities 
with 2,5G (redundant). This not a "research network" per se, it's the 
"production" network for the universities. If I suceeed with this, the 
next challenge (no kidding) is to try the same thing over the commodity 
Internet from here to California (or sonething similar), showing that You 
don't need a "private" network for high speed communication if You do 
things right. After that I've thought of testing against Japan or New 
Zealand, which is about as far You can get from here :-)


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