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Date:      Fri, 11 Apr 2003 18:24:09 +0200
From:      Borje Josefsson <bj@dc.luth.se>
To:        Terry Lambert <tlambert2@mindspring.com>
Cc:        David Gilbert <dgilbert@velocet.ca>
Subject:   Re: tcp_output starving -- is due to mbuf get delay? 
Message-ID:  <200304111624.h3BGO9Kl087165@dc.luth.se>
In-Reply-To: Your message of Fri, 11 Apr 2003 09:08:19 PDT. <3E96E873.9CC19544@mindspring.com> 

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On Fri, 11 Apr 2003 09:08:19 PDT Terry Lambert wrote:

> Mattias Pantzare wrote:
> > Terry Lambert wrote:
> > > Latency =3D pool retention time =3D queue size
> > =

> > Then explain this, FreeBSD to FreeBSD on that link uses all CPU on th=
e
> > sender, the reciver is fine, but performance is not. NetBSD to FreeBS=
D
> > fills the link (1 Gbit/s). On the same computers. MTU 4470. Send and
> > receive maximum windows where tuned to the same values on NetBSD and
> > FreeBSD.
> =

> I rather expect that the number of jumbogram buffers on FreeBSD is
> tiny and/or your MTU is not being properly negotiated between the
> endpoints, and you are fragging the bejesus out of your packets.

Both endpoints have MTU set to 4470, as have all the routers inbetween. =

"traceroute -n -Q 1 -q 1 -w 1 -f remotehost 4470" and netstat both report=
s =

4470.
 =

> 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?

> 	o	Clean boot of FreeBSD target
> 	o	Run FreeBSD against it
> 	o	Save statistics
> 	o	Compare saved statistics of NetBSD vs. FreeBSD
> 		against the target machine
> =

> > And packet loss will affect the performance diffrently if you have a
> > large bandwith-latency product.
> =

> 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 may want to
> disable fast restart on the FreeBSD sender.

Which OID is that?

As a side note, I tried to set tcp.inflight_enable, but that made things =

much worse.

--B=F6rje



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