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

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Message-ID: <Pine.LNX.4.63.0801311340270.14403@trinity.phys.uwm.edu>
Date:	Thu, 31 Jan 2008 13:48:37 -0600 (CST)
From:	Bruce Allen <ballen@...vity.phys.uwm.edu>
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
cc:	"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 Auke,

>> Based on the discussion in this thread, I am inclined to believe that
>> lack of PCI-e bus bandwidth is NOT the issue.  The theory is that the
>> extra packet handling associated with TCP acknowledgements are pushing
>> the PCI-e x1 bus past its limits.  However the evidence seems to show
>> otherwise:
>>
>> (1) Bill Fink has reported the same problem on a NIC with a 133 MHz
>> 64-bit PCI connection.  That connection can transfer data at 8Gb/s.
>
> That was even a PCI-X connection, which is known to have extremely good latency
> numbers, IIRC better than PCI-e? (?) which could account for a lot of the
> latency-induced lower performance...
>
> also, 82573's are _not_ a serverpart and were not designed for this 
> usage. 82546's are and that really does make a difference.

I'm confused.  It DOESN'T make a difference! Using 'server grade' 82546's 
on a PCI-X bus, Bill Fink reports the SAME loss of throughput with TCP 
full duplex that we see on a 'consumer grade' 82573 attached to a PCI-e x1 
bus.

Just like us, when Bill goes from TCP to UDP, he gets wire speed back.

Cheers,
 	Bruce
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