tcp_output starving -- is due to mbuf get delay?

jayanth jayanth at
Thu Apr 10 14:56:49 PDT 2003

You can probably try netstat -s -p ip and look at the 
"output packets dropped due to no bufs, etc." value.


Mike Silbersack (silby at wrote:
> On Thu, 10 Apr 2003, Borje Josefsson wrote:
> > > > Have you tried running kernel profiling yet?  It would be interesting to
> > > > see which functions are using up the largest amount of time.
> >
> > Could do that if I knew how... Not before the weekend though, right now
> > I'm at the longue at the airport...
> I believe that the manpages regarding how to set it up were pretty useful,
> it didn't take me long to get it operational last time I tried.  However,
> that was a while ago, so I can't give you any helpful tips.
> > If everything is OK (which it apparently isn't), top will show free CPU,
> > and netstat should show a *very* steady packet flow (around 90kpps if You
> > have MTU 1500). Any packet loss is fatal for this speed, so if there is a
> > way (as indicated by Mike above) to not restarting with windowsize from
> > scratch that will make recovery much better.
> Well, the packet loss I pointed out would be due to the ifqueue
> overflowing, which could concieveably happen even if the actual network
> wasn't congested.  I don't have the equipment to create such a situation,
> but it sounds like you might, in which case adding a debug printf or a
> counter to see if it's happening might be advantageous.
> Mike "Silby" Silbersack
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