Subject: Re: intel 82599 multi-port performance

From: Chris Friesen <[email-masked]>
Date: Tue, 27 Sep 2011 16:57:33 -0600

On 09/27/2011 11:14 AM, Alexander Duyck wrote:

> This more or less confirms what I was thinking. You are likely hitting
> the PCIe limits of the adapters. The overhead for 64 byte packets is too
> great and as a result you are exceeding the PCIe bandwidth available to
> the adapter. In order to achieve line rate on both ports you would
> likely need to increase your packet size to something along the lines of
> 256 bytes so that the additional PCIe overhead only contributes 50% or
> less to the total PCIe traffic across the bus. Then the 2.5Gb/s of
> network traffic should consume less than 4.0GT/s of PCIe traffic.

For some further information, according to the information here:

http://shader.kaist.edu/packetshader/io_engine/benchmark/i3.html

a dual-port 82599 controller with an i3 CPU can in fact handle sending 
*or* receiving (and then dropping) full line rate on both ports for 
minimum-sized packets.  It can't do both though.  The CPU used in tose 
tests isn't the greatest however, so it's tough to say where the 
bottleneck is.

Chris

-- 
Chris Friesen
Software Developer
GENBAND
[email-masked]
www.genband.com