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

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Message-ID: <47A217CE.4000002@intel.com>
Date:	Thu, 31 Jan 2008 10:47:42 -0800
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Rick Jones <rick.jones2@...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

Rick Jones wrote:
>> 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...

that would be a hardware profiling thing and highly dependent on the part sticking
out of the slot, vendor bus implementation etc... Perhaps Intel has some tools for
this already but I personally do not know of any :/

Auke
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