[dm-devel] RCU-ified dm-mpath for testing/review

[Mike Snitzer]

On Wed, Feb 10 2016 at  8:50pm -0500,
Mike Snitzer <snitzer at redhat.com> wrote:

> On Tue, Feb 09 2016 at  7:45pm -0500,
> Mike Snitzer <snitzer at redhat.com> wrote:
> 
> > 
> > OK, I took a crack at embracing RCU.  Only slightly better performance
> > on my single NUMA node testbed.  (But I'll have to track down a system
> > with multiple NUMA nodes to do any justice to the next wave of this
> > optimization effort)
> > 
> > This RCU work is very heavy-handed and way too fiddley (there could
> > easily be bugs).  Anyway, please see:
> > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=devel2&id=d80a7e4f8b5be9c81e4d452137623b003fa64745
> > 
> > But this might give you something to build on to arrive at something
> > more scalable?
> 
> I've a bit more polished version of this work (broken up into multiple
> commits, with some fixes, etc) here:
> http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/log/?h=devel3
> 
> Hannes and/or Sagi, if you get a chance to try this on your NUMA system
> please let me know how it goes.

FYI, with these changes my single NUMA node testbed's read IOPs went
from:

 ~1310K to ~1410K w/ nr_hw_queues dm-mq=4 and null_blk=4
 ~1330K to ~1415K w/ nr_hw_queues dm-mq=4 and null_blk=12
 ~1365K to ~1425K w/ nr_hw_queues dm-mq=12 and null_blk=12