[openib-general] Re: IPoIB Path Static Rate

[Hal Rosenstock]

On Sat, 2004-12-18 at 10:46, Roland Dreier wrote:
>     Hal> From Woody's MPI data (logs in
>     Hal> http://openib.org/pipermail/openib-general/2004-December/007167.html),
>     Hal> there appear to be some numbers above 1x to me. 1x is 2.5
>     Hal> Gbps minus signalling is really a 2 Gbps data rate. There are
>     Hal> numbers in the log in excess of 350 MBytes/sec which is 2.6
>     Hal> Gbps.
> 
> Fair enough but I still don't think there are many fabrics right now
> where not setting static rate for IPoIB will even be required, let
> alone have a practical effect.

Agreed.

> I don't object in principle to doing this right, it just seems like a
> fair bit of work to write code to retrieve the local PortInfo to get
> the active link speed and link width so that we can calculate our
> local rate and get the right IPD.

Link speed active (other than locked at 2.5 Gbps) was added at IBA 1.2. 

> To solve this, do you think it makes sense to add the active link
> speed and link width to struct ib_port_attr so that it's easy for ULPs
> to get them?  Otherwise ULPs would have to do their own PortInfo queries.

That makes sense to me. There's one catch: since link width/speed active
can change under the covers, this info cannot be cached by the
application or there needs to be a tie in to an event for either of
these (1.2) or link width active (1.1) changing.

-- Hal