Re: [PATCH 0/3] Provide more fine grained control over multipathing

From: Christoph Hellwig
Date: Wed Jun 06 2018 - 05:44:20 EST

On Tue, Jun 05, 2018 at 03:57:05PM -0700, Roland Dreier wrote:
> That makes sense but I'm not sure it covers everything. Probably the
> most common way to do NVMe/RDMA will be with a single HCA that has
> multiple ports, so there's no sensible CPU locality. On the other
> hand we want to keep both ports to the fabric busy. Setting different
> paths for different queues makes sense, but there may be
> single-threaded applications that want a different policy.
> I'm not saying anything very profound, but we have to find the right
> balance between too many and too few knobs.

Agreed. And the philosophy here is to start with a as few knobs
as possible and work from there based on actual use cases.
Single threaded applications will run into issues with general
blk-mq philosophy, so to work around that we'll need to dig deeper
and allow borrowing of other cpu queues if we want to cater for that.