[openib-general] ibstatus support for speed

[Hal Rosenstock]

On Mon, 2006-10-30 at 17:29, Michael Krause wrote:
> 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%. 

Yes of course. It's just a simple diagnostic to display the width and
speed simply.

> If the goal is 
> provide a true indication of the maximum peak bandwidth that an application 
> might see,

That's not the goal of this simplistic tool.

>  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.

Agreed but this is a different issue from what the tool is for.

IMO this issue largely started when IB decided to use the signalling
rate rather than the data rate like most other networks.

-- Hal

> Mike 
> 
>