[openib-general] Re: problem with SDP/AIO on mem-free HCA

[Fab Tillier]

> From: Roland Dreier [mailto:roland at topspin.com]
> Sent: Friday, April 01, 2005 8:27 AM
> 
>     Fab> If you are blessed with a Tavor PRM, see section 8.2.1.6 (in
>     Fab> PRM 1.0.0).  It states that a length of zero in a data
>     Fab> segment indicates a 2GB transfer (MSb is used as a flag to
>     Fab> indicate normal vs. inline data segments).  A zero-byte
>     Fab> request must not reference any data segments.
> 
> Yup, that must be the problem.  I guess mthca can skip over 0-length
> data segments.  Another option would be to say that such work requests
> aren't allowed.  Not sure which way I think we should go.  I need to
> talk to Libor and find out why SDP is generating such requests.
> 

If the overhead of checking for zero-length is negligible, I would recommend
trapping this in mthca.  My reasoning is that unless the IB spec states that
0-length operations can't have data segments, this is a HW specific
limitation and should be handled within the driver.

- Fab