Date: Mon, 14 Apr 2003 06:55:12 -0000 From: Mike Silbersack <silby@silby.com> To: Hiten Pandya <hiten@unixdaemons.com> Cc: freebsd-hackers@freebsd.org Subject: Re: tcp_output starving -- is due to mbuf get delay? Message-ID: <20030413204451.V93049@odysseus.silby.com> In-Reply-To: <20030412195711.GA30459@unixdaemons.com> References: <200304101311.h3ADBgjY022790@samson.dc.luth.se> <20030412195711.GA30459@unixdaemons.com>
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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:
>
> Cheers.
>
> -- 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
benefit.
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
if_output failures.
But I'm too busy to worry about them for now. :)
Mike "Silby" Silbersack
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