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

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Date:	Wed, 30 Jan 2008 09:36:53 -0800
From:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
To:	"Bruce Allen" <ballen@...vity.phys.uwm.edu>,
	<netdev@...r.kernel.org>
Cc:	"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

Bruce Allen wrote:
> Details:
> Kernel version: 2.6.23.12
> ethernet NIC: Intel 82573L
> ethernet driver: e1000 version 7.3.20-k2
> motherboard: Supermicro PDSML-LN2+ (one quad core Intel Xeon X3220,
> Intel 3000 chipset, 8GB memory)

Hi Bruce,
The 82573L (a client NIC, regardless of the class of machine it is in)
only has a x1 connection which does introduce some latency since the
slot is only capable of about 2Gb/s data total, which includes overhead
of descriptors and other transactions.  As you approach the maximum of
the slot it gets more and more difficult to get wire speed in a
bidirectional test.
 
> The test was done with various mtu sizes ranging from 1500 to 9000,
> with ethernet flow control switched on and off, and using reno and
> cubic as a TCP congestion control.

As asked in LKML thread, please post the exact netperf command used to
start the client/server, whether or not you're using irqbalanced (aka
irqbalance) and what cat /proc/interrupts looks like (you ARE using MSI,
right?)

I've recently discovered that particularly with the most recent kernels
if you specify any socket options (-- -SX -sY) to netperf it does worse
than if it just lets the kernel auto-tune.
 
> The behavior depends on the setup. In one test we used cubic
> congestion control, flow control off. The transfer rate in one
> direction was above 0.9Gb/s while in the other direction it was 0.6
> to 0.8 Gb/s. After 15-20s the rates flipped. Perhaps the two steams
> are fighting for resources. (The performance of a full duplex stream
> should be close to 1Gb/s in both directions.)  A graph of the
> transfer speed as a function of time is here:
> https://n0.aei.uni-hannover.de/networktest/node19-new20-noflow.jpg 
> Red shows transmit and green shows receive (please ignore other
> plots): 

One other thing you can try with e1000 is disabling the dynamic
interrupt moderation by loading the driver with
InterruptThrottleRate=8000,8000,... (the number of commas depends on
your number of ports) which might help in your particular benchmark.

just for completeness can you post the dump of ethtool -e eth0 and lspci
-vvv?

Thanks,
  Jesse
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