Date: Thu, 10 Apr 2003 11:16:36 -0500 From: Eric Anderson <anderson@centtech.com> To: Mike Silbersack <silby@silby.com> Cc: freebsd-hackers@freebsd.org Subject: Re: tcp_output starving -- is due to mbuf get delay? Message-ID: <3E9598E4.2000601@centtech.com> References: <200304101311.h3ADBgjY022790@samson.dc.luth.se> <20030410114227.A472@odysseus.silby.com>
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Mike Silbersack wrote:
>>My hosts are connected directly to core routers in a 10Gbps nationwide
>>network, so if anybody is interested in some testing I am more than
>>willing to participate. If anybody produces a patch, I have a third system
>>that I can use for piloting of that too.
>>
>>--Börje
>
>
> This brings up something I've been wondering about, which you might want
> to investigate:
>
>>From tcp_output:
>
> if (error == ENOBUFS) {
> if (!callout_active(tp->tt_rexmt) &&
> !callout_active(tp->tt_persist))
> callout_reset(tp->tt_rexmt, tp->t_rxtcur,
> tcp_timer_rexmt, tp);
> tcp_quench(tp->t_inpcb, 0);
> return (0);
> }
>
> 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.
>
> Have you tried running kernel profiling yet? It would be interesting to
> see which functions are using up the largest amount of time.
It's interesting - I'm only getting about 320mb/s.. I must be hitting a
similar problem. I'm not nearly as adept at hacking code to find bugs
though. :(
Eric
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Eric Anderson Systems Administrator Centaur Technology
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