[PATCH v3 0/9] xen-block: support multi hardware-queues/rings

[Bob Liu <bob.liu@oracle.com>]

Note: These patches were based on original work of Arianna's internship for
GNOME's Outreach Program for Women.

The first patch which just convert xen-blkfront driver to use blk-mq api has
been applied by David.

After using blk-mq api, a guest has more than one(nr_vpus) software request
queues associated with each block front. These queues can be mapped over several
rings(hardware queues) to the backend, making it very easy for us to run
multiple threads on the backend for a single virtual disk.

By having different threads issuing requests at the same time, the performance
of guest can be improved significantly in the end.

Test was done based on null_blk driver:
dom0: v4.2-rc8 16vcpus 10GB "modprobe null_blk"
domu: v4.2-rc8 16vcpus 10GB

[test]
rw=read or randread
direct=1
ioengine=libaio
bs=4k
time_based
runtime=30
filename=/dev/xvdb
numjobs=16
iodepth=64
iodepth_batch=64
iodepth_batch_complete=64
group_reporting

Seqread:
	dom0 	domU(no_mq) 	domU(4 queues) 	 8 queues 	16 queues
iops:  1308k        690k        1380k(+200%)        1238k           1471k

Randread:
	dom0 	domU(no_mq) 	domU(4 queues) 	 8 queues 	16 queues
iops:  1310k        279k        810k(+200%)          871k           1000k

Only with 4queues, iops for domU get improved a lot and nearly catch up with
dom0. There were also similar huge improvement for write and real SSD storage.

---
v3: Rebased to v4.2-rc8

Bob Liu (9):
  xen-blkfront: convert to blk-mq APIs
  xen-block: add document for mutli hardware queues/rings
  xen/blkfront: separate per ring information out of device info
  xen/blkfront: pseudo support for multi hardware queues/rings
  xen/blkfront: convert per device io_lock to per ring ring_lock
  xen/blkfront: negotiate the number of hw queues/rings with backend
  xen/blkback: separate ring information out of struct xen_blkif
  xen/blkback: pseudo support for multi hardware queues/rings
  xen/blkback: get number of hardware queues/rings from blkfront

 drivers/block/xen-blkback/blkback.c |  373 +++++-----
 drivers/block/xen-blkback/common.h  |   53 +-
 drivers/block/xen-blkback/xenbus.c  |  376 ++++++----
 drivers/block/xen-blkfront.c        | 1343 ++++++++++++++++++++---------------
 include/xen/interface/io/blkif.h    |   32 +
 5 files changed, 1278 insertions(+), 899 deletions(-)

-- 
1.7.10.4