[Bridge] Rx Buffer sizes on e1000

Leigh Sharpe lsharpe at pacificwireless.com.au
Tue Nov 13 15:20:37 PST 2007


>I find regular PCI bus (32bit) tops out at about 600 Mbits/sec on most
>machines. For PCI-X (64 bit/133) a realistic value is 6 Gbits/sec. The
>problem is arbitration and transfer sizes. 

>That means for for normal PCI32, one gigabit card or 
>6 100Mbit Ethernet interfaces can saturate the bus. Also, all that
>I/O slows down the CPU and memory interface.

I'm seeing issues with only 110Mbits/sec of traffic. Ultimately I expect
to be using far more than that, but I really didn't expect to be
overloading the bus yet.

Leigh.

-----Original Message-----
From: Stephen Hemminger [mailto:shemminger at linux-foundation.org] 
Sent: Wednesday, 14 November 2007 9:47 AM
To: Leigh Sharpe
Cc: bridge at lists.linux-foundation.org
Subject: Re: [Bridge] Rx Buffer sizes on e1000


I find regular PCI bus (32bit) tops out at about 600 Mbits/sec on most
machines. For PCI-X (64 bit/133) a realistic value is 6 Gbits/sec. The
problem is arbitration and transfer sizes.

Absolute limit is:
PCI32 33MHz = 133MB/s
PCI32 66MHz = 266MB/s
PCI64 33MHz = 266MB/s
PCI64 66MHz = 533MB/s
PCI-X 133MHz = 1066MB/s 

That means for for normal PCI32, one gigabit card or 
6 100Mbit Ethernet interfaces can saturate the bus. Also, all that
I/O slows down the CPU and memory interface.


-- 
Stephen Hemminger <shemminger at linux-foundation.org>



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