tcp_output starving -- is due to mbuf get delay?
silby at silby.com
Sun Apr 13 23:55:12 PDT 2003
On Sat, 12 Apr 2003, Hiten Pandya wrote:
> > That tcp_quench knocks the window size back to one packet, if I'm not
> > mistaken. You might want to put a counter there and see if that's
> > happening frequently to you; if so, it might explain some loss of
> > performance.
> Maybe something like this:
> -- Hiten
As Jayanth pointed out, ip_output already keeps statistics on when it
returns ENOBUFS, so adding this additional variable wouldn't be of much
For reference (from netstat -s):
0 output packets dropped due to no bufs, etc.
Although, I think ip_output could be improved. It precalculates the
expected # of packets to be sent, and returns ENOBUFS early if its
estimate looks bad. However, if it gets to the point where if_output is
called, and if_output then fails, no statistic is kept. So, it does look
like Hiten's patch could be useful, as well as another counter tracking
But I'm too busy to worry about them for now. :)
Mike "Silby" Silbersack
More information about the freebsd-performance