[openib-general] Re: RMPP

[Sean Hefty]

Hal Rosenstock wrote:
> In addition to passing the hdr_len and data_len to ib_create_send_mad: 
>                 rmpp_mad->rmpp_hdr.paylen_newwin = cpu_to_be32(hdr_len -
>                         offsetof(struct ib_rmpp_mad, data) + data_len);
> That's not the "real" payload length that would go into the packet; just
> one segment's worth of class header. Correct ?
> 
> If the above is correct, I'm not sure the actual payload lengths in the
> DATA packets are correct. I also see the padding on the last segment of
> a multipacket send not cleared (I integrated the part of your patch
> relating to the pad calculation).

Running grmpp and using madeye to check the packets, I ran 3 tests:

user-data size	payload 1st in segment	payload in last segment
1200		1320 (220x6)		124
50		54			54
580		660 (220x3)		152

For multi-packet segments, I think that the payload in the 1st segment will 
always be a multiple of 220 bytes (256 - sizeof common MAD header - sizeof 
RMPP header).  For the tests that I ran, these appear to be correct.

Since grmpp uses vendor MADs, it can transfer 216 bytes of user-data per 
segment.  Using the 580 example, the data is segmented into 216 + 216 + 148 
bytes.  The payload in the last segment includes the extra 4 byte vendor 
specific header.  Likewise, 1200 = 216 x 5 + 120, with an extra 4 bytes 
added for the header.

I haven't looked at why the data isn't cleared yet, but will do so next. 
The memory allocations in create_send_mad look right to me...

- Sean