[openib-general] [RFC] static rate: encoding definition

[Jack Morgenstein]

Static rate encoding is not currently explicitly defined in the verbs layer.  
IPoIB takes the definition to be the IPD (interpacket delay) as described in 
the IB Spec section 9.11.

However, a static rate encoding is given in the PathRecord (rate field in 
Table 205 on page 901, section 15.2.5.6 of IB Spec).

This is the encoding that should be used in the verbs layer.

All mappings to/from static rate (as in the PathRecord) to IPD properly belong 
in the provider layer -- so that they are performed only once (and not in 
every ULP).

Until now, this was not such an issue, because multiple static rates were not 
really available -- everyone basically used 4X.

This, however, is changing.  8X is already available, and higher rates will 
surely follow.

The time to implement this change in approach is NOW -- before use of higher 
rates becomes widespread.

The two static rate patches (one for kernel space, one for userspace) show 
changes needed in the verbs, sa and ULP layers:
[PATCH 1 of 2] static rate encoding change (kernel)
[PATCH 2 of 2] static rate encoding change (user)

If the community agrees, we will follow up with changes at the provider level.