[RFC][CFT] GEOM direct dispatch and fine-grained CAM locking

[Johan Hendriks]

Alexander Motin wrote:
> Hi.
>
> I would like to invite more people to review and test my patches for 
> improving CAM and GEOM scalability, that for last six months you could 
> see developing in project/camlock SVN branch. Full diff of that branch 
> against present head (r255131) can be found here:
> http://people.freebsd.org/~mav/camlock_patches/camlock_20130902.patch
>
> Heavy CAM changes there were focused on reducing scope of SIM lock to 
> only protecting SIM internals, but not CAM core. That allows many 
> times reduce lock congestion, especially on heavily parallel request 
> submission with GEOM changes below. More detailed description of 
> changes you could see here earlier:
> http://docs.freebsd.org/cgi/mid.cgi?520D4ADB.50209
>
> GEOM changes were focused on avoiding switching to GEOM up/down 
> threads in relatively simple setups where respective classes don't 
> require it (and were explicitly marked so). That allows save on 
> context switches and on systems with several HBAs and disks talk to 
> them concurrently (that is where CAM locking changes are handy). Such 
> classes were modified to support it: DEV, DISK, LABEL, MULTIPATH, NOP, 
> PART, RAID (partially), STRIPE, ZERO, VFS, ZFS::VDEV, ZFS::ZVOL and 
> some others. Requests to/from other classes will be queued to GEOM 
> threads same as before.
>
> Together that allows to double block subsystem performance on high (at 
> least 100-200K) IOPS benchmarks, allowing to reach up to a million 
> total IOPS, while keeping full compatibility with all major ABIs/KBIs.
>
> Since we are already in 10.0 release process and changes are quite 
> big, my plan is to wait and commit them to head branch after the 
> freeze end, and then merge to stable/10.  I hope the release process 
> will go on schedule to not delay this work for another six months.
>
> This work is sponsored by iXsystems, Inc.
>
Hello i would like to test this patch set.
But how can i stress the machine, do you have a script or something i 
can use to make the system do heavy I/O on the disks!

regards
Johan