linux-kernel - Re: e1000 full-duplex TCP performance well below wire speed

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Date:	Wed, 30 Jan 2008 14:33:35 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Bruce Allen <ballen@...vity.phys.uwm.edu>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: e1000 full-duplex TCP performance well below wire speed

On Wed, 30 Jan 2008 16:25:12 -0600 (CST)
Bruce Allen <ballen@...vity.phys.uwm.edu> wrote:

> Hi Stephen,
> 
> Thanks for your helpful reply and especially for the literature pointers.
> 
> >> Indeed, we are not asking to see 1000 Mb/s.  We'd be happy to see 900
> >> Mb/s.
> >>
> >> Netperf is trasmitting a large buffer in MTU-sized packets (min 1500
> >> bytes).  Since the acks are only about 60 bytes in size, they should be
> >> around 4% of the total traffic.  Hence we would not expect to see more
> >> than 960 Mb/s.
> 
> > Don't forget the network overhead: http://sd.wareonearth.com/~phil/net/overhead/
> > Max TCP Payload data rates over ethernet:
> >  (1500-40)/(38+1500) = 94.9285 %  IPv4, minimal headers
> >  (1500-52)/(38+1500) = 94.1482 %  IPv4, TCP timestamps
> 
> Yes.  If you look further down the page, you will see that with jumbo 
> frames (which we have also tried) on Gb/s ethernet the maximum throughput 
> is:
> 
>    (9000-20-20-12)/(9000+14+4+7+1+12)*1000000000/1000000 = 990.042 Mbps
> 
> We are very far from this number -- averaging perhaps 600 or 700 Mbps.
>


That is the upper bound of performance on a standard PCI bus (32 bit).
To go higher you need PCI-X or PCI-Express. Also make sure you are really
getting 64-bit PCI, because I have seen some e1000 PCI-X boards that
are only 32bit.
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