[openib-general] Re: Some Initial RMPP Comments and Questions

[Sean Hefty]

Hal Rosenstock wrote:

> Hi Sean,
> 
> I just started playing with RMPP and have one comment and a couple of
> questions. I am just doing some preliminary testing with SA
> GetTable/GetTableResp.
> 
> 1. I see a NWL in some ACKs of 0x41 when ACKing segment 1. So the
> receive side supports 64 incoming MADs. Is that correct ? (That seems
> good to me).

This is set in the call window_size().  The window size is set to the 
size of the QP >> 3.  I made this value up.

> 2. Since RMPP supports streaming (I know OpenIB doesn't do this on
> transmit), what does the receiver do with an incoming RMPP stream whose
> PayloadLength is not specified in the FIRST DATA packet ? (I think this
> may be needed for interoperability with third party RMPP implementations
> which do this).

The RMPP receive code doesn't use the FIRST payload length when 
receiving data.  It looks for the LAST bit to be set in the incoming 
data MAD.

Also, if you can think of a way to support this on the send side, 
you/I/someone could add this.  I think that this would require 
extending the send MAD API.

> 3. How does the RMPP receiver handle discrepancies between the FIRST
> DATA PayloadLength and the LAST DATA PayloadLength ?

Currently it doesn't.  The payload length in the LAST data packet is 
used to calculate the padding for the total MAD length.  See 
get_mad_len().  The only check that's done is to ensure that the 
calculated padding is smaller than the MAD's data size.

- Sean