Re: [PATCH V6 9/9] isert: Support iWARP transports using FRMRs

[Sagi Grimberg <sagig@dev.mellanox.co.il>]

On 7/24/2015 10:24 PM, Jason Gunthorpe wrote:
> On Fri, Jul 24, 2015 at 01:48:09PM -0500, Steve Wise wrote:
>>> The use of FRWR for RDMA READ should be iWarp specific, IB shouldn't
>>> pay that overhead. I am expecting to see a cap_rdma_read_rkey or
>>> something in here ?
>>
>> Ok.  But cap_rdma_read_rkey() doesn't really describe the
>> requirement.  The requirement is rkey + REMOTE_WRITE.  So it is more
>> like rdma_cap_read_requires_remote_write() which is ugly and too
>> long (but descriptive)...
>
> I don't care much what name you pick, just jam something like this in
> the description

I think we can just do if (signature || iwarp) use fastreg else
use local_dma_lkey.

>
>   If set then RDMA_READ must be performed by mapping the local
>   buffers through a rkey MR with ACCESS_REMOTE_WRITE enabled.
>   The rkey of this MR should be passed in as the sg_lists's lkey for
>   IB_WR_RDMA_READ_WITH_INV.

I think this would be an incremental patch and not as part of iwarp
support.

Question though, wouldn't it be better to do a single RDMA_READ to say
4 registered keys rather than RDMA_READ_WITH_INV for each?