Re: FW: [PATCH for 2.6.25] SVCRDMA: Use only 1 RDMA read scatter entry for iWARP adapters

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Mar 24, 2008 at 09:57:04AM -0700, Roland Dreier wrote:
>  > Will do, thanks, but, as a subsequent patch, could we clean this up a
>  > little?  For example, assuming sge_count and sc_max_sge are always
>  > positive, isn't the (sge_count > 1) check superfluous, given that the
>  > following min_t's going to produce 1 in that case anyway?
> 
> Yes, I had the same thought reading the code but I didn't want to try
> and do too many things in one patch.

Sure.

> 
>  > Also, would it be possible just to ensure sc_max_sge is just set to 1
>  > from the start in this case?
> 
> I think the problem with this is that on InfiniBand, it is fine to
> have multiple scatter entries for an RDMA read request, while on iWARP
> only 1 scatter entry is possible for RDMA read.  For both IB and
> iWARP, you can eg have multiple gather entries for an RDMA write.  So
> sc_max_sge as it stands may want to be bigger than 1 even for iWARP devices.
> 
> One not-too-bad possibility would just be to have sc_max_sge and
> sc_max_sge_rdma_read fields and initialize them properly based on IB
> vs iWARP...

I'll leave the decision to people who understand this code better than
me, but offhand that does sound like it'd be a little more
straightforward.

--b.