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

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Date:	Wed, 30 Jan 2008 16:33:26 -0600 (CST)
From:	Bruce Allen <ballen@...vity.phys.uwm.edu>
To:	Ben Greear <greearb@...delatech.com>
cc:	netdev@...r.kernel.org,
	Carsten Aulbert <carsten.aulbert@....mpg.de>,
	Henning Fehrmann <henning.fehrmann@....mpg.de>,
	Bruce Allen <bruce.allen@....mpg.de>
Subject: Re: e1000 full-duplex TCP performance well below wire speed

Hi Ben,

Thank you for the suggestions and questions.

>> We've connected a pair of modern high-performance boxes with integrated 
>> copper Gb/s Intel NICS, with an ethernet crossover cable, and have run some 
>> netperf full duplex TCP tests.  The transfer rates are well below wire 
>> speed.  We're reporting this as a kernel bug, because we expect a vanilla 
>> kernel with default settings to give wire speed (or close to wire speed) 
>> performance in this case. We DO see wire speed in simplex transfers. The 
>> behavior has been verified on multiple machines with identical hardware.
>
> Try using NICs in the pci-e slots.  We have better luck there, as you 
> usually have more lanes and/or higher quality NIC chipsets available in 
> this case.

It's a good idea.  We can try this, though it will take a little time to 
organize.

> Try a UDP test to make sure the NIC can actually handle the throughput.

I should have mentioned this in my original post -- we already did this.

We can run UDP wire speed full duplex (over 900 Mb/s in each direction, at 
the same time). So the problem stems from TCP or is aggravated by TCP. 
It's not a hardware limitation.

> Look at the actual link usage as reported by the ethernet driver so that 
> you take all of the ACKS and other overhead into account.

OK.  We'll report on this as soon as possible.

> Try the same test using 10G hardware (CX4 NICs are quite affordable 
> these days, and we drove a 2-port 10G NIC based on the Intel ixgbe 
> chipset at around 4Gbps on two ports, full duplex, using pktgen). As in 
> around 16Gbps throughput across the busses.  That may also give you an 
> idea if the bottleneck is hardware or software related.

OK.  That will take more time to organize.

Cheers,
 	Bruce
>
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