[Nottingham] Network TCP Tuning for Fast Links

Duncan John Fyfe djf at star.le.ac.uk
Tue May 29 10:45:34 BST 2007

On Sun, 2007-05-27 at 23:48 +0100, Martin wrote:
> Folks,
> >From a little reading around for why you can't get 1 Gbit/s down a Gbit
> network and...
> Using "fast" links, or even for internal networks, there
> can be some performance gains from tuning system TCP settings.
> A few links I've just scanned through are:
> http://dsd.lbl.gov/TCP-tuning/background.html
> http://dsd.lbl.gov/TCP-tuning/linux.html
> http://proj.sunet.se/E2E/tcptune.html
> http://www.onlamp.com/pub/a/onlamp/2005/11/17/tcp_tuning.html?page=1
> http://www.psc.edu/networking/projects/tcptune/
> http://www.acc.umu.se/~maswan/linux-netperf.txt
> http://datatag.web.cern.ch/datatag/howto/tcp.html
> http://www.aarnet.edu.au/engineering/networkdesign/mtu/local.html
> http://www.hep.ucl.ac.uk/~ytl/tcpip/linux/txqueuelen/
> And for bonding multiple links/interfaces:
> http://www.linux-corner.info/bonding.html
> http://www.devco.net/archives/2004/11/26/linux_ethernet_bonding.php
> The short story is that you can greatly improve your data transfer rate
> over long internet links by increasing the system TCP tx and rx
> window/buffer values. Note also the comments in
> http://www.onlamp.com/pub/a/onlamp/2005/11/17/tcp_tuning.html?page=1
> about software set buffer sizes.
> For internal networks fully under your control, you can greatly increase
> transfer rates and reduce CPU overheads by using "Jumbo packets" with an
> MTU of 9000. (Most new switches should support that. Check further
> before trying to go any larger.)

If you have not come across them before can I recommend articles linked
from this page:

In fact a trawl round http://www.clustermonkey.net/
provides a veritable treasure trove of well written documents on
everything to do with system performance.

Have fun,

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