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Subject[RFC PATCH 00/10] Multi-queue support for xen-block driver
This patchset convert the Xen PV block driver to the multi-queue block layer API
by sharing and using multiple I/O rings between the frontend and backend.

It's based on the result of Arianna's internship for GNOME's Outreach Program
for Women, in which she was mentored by Konrad Rzeszutek Wilk. I also worked on
this patchset with her at that time, and now fully take over this task.
I've got her authorization to "change authorship or SoB to the patches as you

A few words on block multi-queue layer:
Multi-queue block layer improved block scalability a lot by split single request
queue to per-processor software queues and hardware dispatch queues. The linux
blk-mq API will handle software queues, while specific block driver must deal
with hardware queues.

The xen/block implementation:
1) Convert to blk-mq api with only one hardware queue.
2) Use more rings to act as multi hardware queues.
3) Negotiate number of hardware queues, the same as xen-net driver. The
backend notify "multi-queue-max-queues" to frontend, then the front write back
final number to "multi-queue-num-queues".

Test result:
fio's IOmeter emulation on a 16 cpus domU with a null_blk device, hardware
queue number was 16.
nr_fio_jobs IOPS(before) IOPS(after) Diff
1 57k 58k 0%
4 95k 201k +210%
8 89k 372k +410%
16 68k 284k +410%
32 65k 196k +300%
64 63k 183k +290%

More results are coming, there was also big improvement on both write-IOPS and

Any comments or suggestions are welcome.
Thank you,
-Bob Liu

Bob Liu (10):
xen/blkfront: convert to blk-mq API
xen/blkfront: drop legacy block layer support
xen/blkfront: reorg info->io_lock after using blk-mq API
xen/blkfront: separate ring information to an new struct
xen/blkback: separate ring information out of struct xen_blkif
xen/blkfront: pseudo support for multi hardware queues
xen/blkback: pseudo support for multi hardware queues
xen/blkfront: negotiate hardware queue number with backend
xen/blkback: get hardware queue number from blkfront
xen/blkfront: use work queue to fast blkif interrupt return

drivers/block/xen-blkback/blkback.c | 370 ++++++++-------
drivers/block/xen-blkback/common.h | 54 ++-
drivers/block/xen-blkback/xenbus.c | 415 +++++++++++------
drivers/block/xen-blkfront.c | 894 +++++++++++++++++++++---------------
4 files changed, 1018 insertions(+), 715 deletions(-)


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