On Fri, Feb 2, 2018 at 5:40 PM, Doug Ledford [off-list ref] wrote:

On Fri, 2018-02-02 at 16:07 +0000, Bart Van Assche wrote:

quoted

On Fri, 2018-02-02 at 15:08 +0100, Roman Pen wrote:

quoted

Since the first version the following was changed:

   - Load-balancing and IO fail-over using multipath features were added.
   - Major parts of the code were rewritten, simplified and overall code
     size was reduced by a quarter.

That is interesting to know, but what happened to the feedback that Sagi and
I provided on v1? Has that feedback been addressed? See also
https://www.spinics.net/lists/linux-rdma/msg47819.html and
https://www.spinics.net/lists/linux-rdma/msg47879.html.

Regarding multipath support: there are already two multipath implementations
upstream (dm-mpath and the multipath implementation in the NVMe initiator).
I'm not sure we want a third multipath implementation in the Linux kernel.

There's more than that.  There was also md-multipath, and smc-r includes
another version of multipath, plus I assume we support mptcp as well.

But, to be fair, the different multipaths in this list serve different
purposes and I'm not sure they could all be generalized out and served
by a single multipath code.  Although, fortunately, md-multipath is
deprecated, so no need to worry about it, and it is only dm-multipath
and nvme multipath that deal directly with block devices and assume
block semantics.  If I read the cover letter right (and I haven't dug
into the code to confirm this), the ibtrs multipath has much more in
common with smc-r multipath, where it doesn't really assume a block
layer device sits on top of it, it's more of a pure network multipath,
which the implementation of smc-r is and mptcp would be too.  I would
like to see a core RDMA multipath implementation soon that would
abstract out some of these multipath tasks, at least across RDMA links,
and that didn't have the current limitations (smc-r only supports RoCE
links, and it sounds like ibtrs only supports IB like links, but maybe
I'm wrong there, I haven't looked at the patches yet).

Hi Doug, hi Bart,

Thanks for your valuable input, here is my 2 cents:

IBTRS multipath is indeed a network multipath, with sysfs interface to
remove/add path dynamically.
IBTRS is built on rdma-cm, so expect to support RoCE and iWARP, but we
mainly tested in IB environment,
slightly tested on RXE.


Regards,
-- 
Jack Wang
Linux Kernel Developer