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

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Date:	Wed, 30 Jan 2008 17:23:08 -0600 (CST)
From:	Bruce Allen <ballen@...vity.phys.uwm.edu>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: e1000 full-duplex TCP performance well below wire speed

Hi Stephen,

>>>> Indeed, we are not asking to see 1000 Mb/s.  We'd be happy to see 900
>>>> Mb/s.
>>>>
>>>> Netperf is trasmitting a large buffer in MTU-sized packets (min 1500
>>>> bytes).  Since the acks are only about 60 bytes in size, they should be
>>>> around 4% of the total traffic.  Hence we would not expect to see more
>>>> than 960 Mb/s.
>>
>>> Don't forget the network overhead: http://sd.wareonearth.com/~phil/net/overhead/
>>> Max TCP Payload data rates over ethernet:
>>>  (1500-40)/(38+1500) = 94.9285 %  IPv4, minimal headers
>>>  (1500-52)/(38+1500) = 94.1482 %  IPv4, TCP timestamps
>>
>> Yes.  If you look further down the page, you will see that with jumbo
>> frames (which we have also tried) on Gb/s ethernet the maximum throughput
>> is:
>>
>>    (9000-20-20-12)/(9000+14+4+7+1+12)*1000000000/1000000 = 990.042 Mbps
>>
>> We are very far from this number -- averaging perhaps 600 or 700 Mbps.

> That is the upper bound of performance on a standard PCI bus (32 bit).
> To go higher you need PCI-X or PCI-Express. Also make sure you are really
> getting 64-bit PCI, because I have seen some e1000 PCI-X boards that
> are only 32bit.

The motherboard NIC is in a PCI-e x1 slot.  This has a maximum speed of 
250 MB/s (2 Gb/s) in each direction.  It should be a factor of 2 more 
interface speed than is needed.

Cheers,
 	Bruce
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