[ofa-general] Re: [PATCH] Request For Comments:

[Steve Wise]

Roland Dreier wrote:
>  > - always do peer2peer and don't let the app choose.  This forces
>  > the overhead of p2p mode on all apps, but preserves the API.
>
> How bad is the overhead?
>
>  - R.
>   
The client side must send a "Ready To Receive" message.  This will be 
negotiated via the MPA exchange and the resulting RTR message may be a 
0B read + read response, 0B write, or a 0B send.  For chelsio, the 0B 
write couldn't be used, and the 0B read was the least impact on the 
driver code, so we used that.  For nes, they currently use a 0B write.

Also, there are some "caveats" if you turn this on:

1) private data is used to negotiate the type of RTR message and if its 
needed.   This is more of a global module option I think, since it will 
break interoperability with iwarp.  Prolly will bump the MPA version 
number if this option is on too.

2) if the RTR message fails, it can generate a CQE that is unexpected.

3) if using SEND, then a recv completion is always generated.

Steve.