netdev - Re: Minimizing TCP latency

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Message-ID: <alpine.DEB.1.10.1003300559040.28550@uplift.swm.pp.se>
Date:	Tue, 30 Mar 2010 06:05:47 +0200 (CEST)
From:	Mikael Abrahamsson <swmike@....pp.se>
To:	Ben Hoyt <benhoyt@...il.com>
cc:	netdev@...r.kernel.org
Subject: Re: Minimizing TCP latency

On Tue, 30 Mar 2010, Ben Hoyt wrote:

> We're currently seeing a round-trip time of about 40us between two
> Linux servers on our network (so presumably about 20us one way).
> Anything quicker than that would be nice, but we're hoping to get down
> to about half that.

Serialisation delay on GigE for a 512 byte packet is 4us if my 
calculations are correct, so if you have some equipment in between that 
means two serialisations either way, meaning on GigE just the 
serialisation delay is 16us RTT.

You'd probably be better off directly connection the two machines with 
10GE NIC, or at least buy equipment that'll do cut-through switching if 
you want to bring the delay down. I'm even surprised you got it down this 
low...

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