[openib-general] RDMA_READ SGE

[Michael S. Tsirkin]

Quoting r. Tom Tucker <tom at opengridcomputing.com>:
> Subject: RDMA_READ SGE
> 
> Roland:
> 
> iWARP RNIC's have a different SGE limit for RDMA_READ response then they
> do for other SGE. To support iWARP, we need to add a max_read_sge
> attribute to the ib_device structure. We had originally mapped this to
> max_sge_rd, but someone pointed out that this is not for RDMA_READ in
> general, but for RDMA_READ_ATOMIC in particular. 
> 
> In any event, we need to add this value to the ib_verbs.h structure so
> that ULP know how to limit sge for the RDMA_READ sink. 
> 
> Do you want me to submit a patch on top of Steve's, or do you want me to
> wait until you've got the git tree built?
> 
> Thanks,
> Tom

Actually, Mellanox devices also have different SGE limits
depending on the operation kinds and QP types.
So far the approach there has been that the device should report
one value for the best case result.

Practically I don't see reporting the exact values as a priority -
I think applications really can figure this out easier by attempting
operating with relevant parameters and fallback to smaller values
on failure.

But assuming that applications really need this information -
it seems we really should generalize this - maybe make the device provide
a function mapping QP attributes and operation kinds to the max set of values
allowed?

-- 
MST