On Wed, Jun 04, 2014 at 07:53:30AM -0700, Christoph Hellwig wrote:

On Wed, Jun 04, 2014 at 10:50:53AM -0400, Tejun Heo wrote:

quoted

Hmmm... the biggest thing is ioscheds.  They heavily rely on being
strongly synchronized and are pretty important for rotating rusts.
Maybe they can be made to work with blk-mq by forcing single queue or
something but do we wnat that?

Jens is planning to add an (optional) I/O scheduler to blk-mq, and
that is indeed required for proper disk support.  I don't think there
even is a need to limit it to a single queue technically, although
devices that support multiple queues are unlikely to need I/O
scheduling.

I think what Jens is planning is something really minimal.  Things
like [cb]fq heavily depend on the old block infrastructure.  I don't
know.  Maybe they can be merged in time but I'm not quite sure we'd
have enough pressure to actually do that.  Host-granular switching
should be good enough, I guess.

Thanks.

-- 
tejun