[openib-general] ibstatus support for speed

[Michael Krause]

At 02:05 PM 10/30/2006, Roland Dreier wrote:
>     Hal> So rate = speed * width ?
>
>Yes, you should see the right think on DDR systems etc.

Strange.  Bandwidth = signaling rate * width.   This of course is raw 
bandwidth prior to encoding, protocol, etc. overheads which will derate the 
effective application bandwidth minimally be 20-25%.   If the goal is 
provide a true indication of the maximum peak bandwidth that an application 
might see, then stating 10 Gbps for an IB x4 SDR is clearly a 
misrepresentation and out of alignment with other networking links such as 
Ethernet which customers understand its bandwidth to be minimally after the 
encoding, etc. is removed from the equation.   The perpetual trend by 
marketing to use 10 Gbps IB as equivalent to 10 Gbps of application data is 
actually detrimental not beneficial when it comes to customers.  It 
inevitably leads to the question of why the application is not achieving 
the stated bandwidth, i.e. why it is say 700-800MB/s theoretical peak for a 
x4 while a 10 GbE is 1 GB/s peak.  So much marketing hype has gone forward 
already.   I realize I'm tilting at windmills but if you are to provide a 
tool that is supposed to project the maximum bandwidth possible and given 
the goal of OFA is to provide as much conceptual commonality with existing 
network stacks / links, then it would be beneficial to have this move 
towards a much more apple-to-apple communication of information.  I know it 
would certainly help with having to repeatedly explain why IB 10 Gbps is 
not the same as 10 GbE to customers and analysts.

Mike