[PATCH] nvme-rdma: Support 2 inline data SGEs for write commands.

[Parav Pandit]

> -----Original Message-----
> From: Christoph Hellwig [mailto:hch at lst.de]
> Sent: Wednesday, February 8, 2017 2:28 AM
> To: Parav Pandit <parav at mellanox.com>
> Cc: hch at lst.de; sagi at grimberg.me; linux-nvme at lists.infradead.org;
> axboe at fb.com; keith.busch at intel.com
> Subject: Re: [PATCH] nvme-rdma: Support 2 inline data SGEs for write
> commands.
> 
> This looks fine to me in general, but I'm a little curious how your arrived at
> that 2 number.  Why not 4 or 8?

Some adapters doesn't support more than 5 sges. So increasing it to 4 or 8 would fail them.
Chuck reported 1 out of 3 adapters only support 3. Its likely due to min(send_sge, recv_sge).
With total of 3 SGEs (64B cmd sge + data sges), WQE fits in 64 bytes size at the provider driver level. So to strike balance between cache line usage and performance, and to be nice to those adapters which has low SGE (either due to min(send_sge, recv) or other otherwise, I picked 2 data sges. 

Side  note: I have split out send and recv sge in other unrelated patch which is in review internally from linux-rdma tree.