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

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Date:	Thu, 31 Jan 2008 10:38:32 -0800
From:	Rick Jones <rick.jones2@...com>
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
CC:	Bruce Allen <ballen@...vity.phys.uwm.edu>,
	"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

> A lot of people tend to forget that the pci-express bus has enough bandwidth on
> first glance - 2.5gbit/sec for 1gbit of traffix, but apart from data going over it
> there is significant overhead going on: each packet requires transmit, cleanup and
> buffer transactions, and there are many irq register clears per second (slow
> ioread/writes). The transactions double for TCP ack processing, and this all
> accumulates and starts to introduce latency, higher cpu utilization etc...

Sounds like tools to show PCI* bus utilization would be helpful...

rick jones
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