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

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Date:	Fri, 1 Feb 2008 01:54:24 -0600 (CST)
From:	Bruce Allen <ballen@...vity.phys.uwm.edu>
To:	Bill Fink <billfink@...dspring.com>
cc:	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	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 Bill,

> I started musing if once one side's transmitter got the upper hand, it 
> might somehow defer the processing of received packets, causing the 
> resultant ACKs to be delayed and thus further slowing down the other 
> end's transmitter.  I began to wonder if the txqueuelen could have an 
> affect on the TCP performance behavior.  I normally have the txqueuelen 
> set to 10000 for 10-GigE testing, so decided to run a test with 
> txqueuelen set to 200 (actually settled on this value through some 
> experimentation).  Here is a typical result:
>
> [bill@...nce4 ~]$ nuttcp -f-beta -Itx -w2m 192.168.6.79 & nuttcp -f-beta -Irx -r -w2m 192.168.6.79
> tx:  1120.6345 MB /  10.07 sec =  933.4042 Mbps 12 %TX 9 %RX 0 retrans
> rx:  1104.3081 MB /  10.09 sec =  917.7365 Mbps 12 %TX 11 %RX 0 retrans
>
> This is significantly better, but there was more variability in the
> results.  The above was with TSO enabled.  I also then ran a test
> with TSO disabled, with the following typical result:
>
> [bill@...nce4 ~]$ nuttcp -f-beta -Itx -w2m 192.168.6.79 & nuttcp -f-beta -Irx -r -w2m 192.168.6.79
> tx:  1119.4749 MB /  10.05 sec =  934.2922 Mbps 13 %TX 9 %RX 0 retrans
> rx:  1131.7334 MB /  10.05 sec =  944.8437 Mbps 15 %TX 12 %RX 0 retrans
>
> This was a little better yet and getting closer to expected results.

We'll also try changing txqueuelen.  I have not looked, but I suppose that 
this is set to the default value of 1000.  We'd be delighted to see 
full-duplex performance that was consistent and greater than 900 Mb/s x 2.

> I do have some other test systems at work that I might be able to try 
> with newer kernels and/or drivers or maybe even with other vendor's GigE 
> NICs, but I won't be back to work until early next week sometime.

Bill, we'd be happy to give you root access to a couple of our systems 
here if you want to do additional testing.  We can put the latest drivers 
on them (and reboot if/as needed).  If you want to do this, please just 
send an ssh public key to Carsten.

Cheers,
 	Bruce
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