[Qemu-devel] [PATCH RFC 00/14] dataplane: performance optimization and multi virtqueue

[Ming Lei <ming.lei@canonical.com>]

Hi,

These patches bring up below 4 changes:

	- introduce selective coroutine bypass mechanism
	for improving performance of virtio-blk dataplane with
	raw format image

	- introduce object allocation pool and apply it to
	virtio-blk dataplane for improving its performance

	- linux-aio changes: fixing for cases of -EAGAIN and partial
	completion, increase max events to 256, and remove one unuseful
	fields in 'struct qemu_laiocb'

	- support multi virtqueue for virtio-blk dataplane

The virtio-blk multi virtqueue feature will be added to virtio spec 1.1[1],
and the 3.17 linux kernel[2] will support the feature in virtio-blk driver.
For those who wants to play the stuff, the kernel side patche can be found
in either Jens's block tree[3] or linux-next[4].

Below fio script running from VM is used for test improvement of these patches:

	[global]
	direct=1
	size=128G
	bsrange=4k-4k
	timeout=120
	numjobs=${JOBS}
	ioengine=libaio
	iodepth=64
	filename=/dev/vdc
	group_reporting=1
	
	[f]
	rw=randread

One quadcore VM is created in below two hosts to run above fio test:

	- laptop(quadcore: 2 physical cores, 2 threads per physical core)
	- server(16cores: 8 physical cores, 2 threads per physical core)

Follows the test result on throughput improvement(IOPS) with
this patchset(2 virtqueues per virito-blk device) against QEMU
2.1.0-rc1:

	---------------------------------------------------
			| VM in server host	| VM in laptop host
	---------------------------------------------------
	JOBS=2	| +21%				| +30%
	---------------------------------------------------
	JOBS=4	| +84%				| +85%
	---------------------------------------------------

>From above result, we can see both scalability and performance
get improved a lot.

After commit 580b6b2aa2(dataplane: use the QEMU block
layer for I/O), average time for submiting one single
request has been increased a lot, as my trace, the average
time taken for submiting one request has been doubled even
though block plug&unplug mechanism is introduced to
ease its effect. That is why this patchset introduces
selective coroutine bypass mechanism and object allocation
pool for saving the time first. Based on QEMU 2.0, only
single virtio-blk dataplane multi virtqueue patch can get
much better improvement than current result[5].

TODO:
	- optimize block layer for linux aio, so that
	more time can be saved for submitting request
	- support more than one aio-context for improving
	virtio-blk performance

 async.c                         |    1 +
 block.c                         |  129 ++++++++++++++++++-----
 block/linux-aio.c               |   93 +++++++++++-----
 block/raw-posix.c               |   34 ++++++
 hw/block/dataplane/virtio-blk.c |  221 ++++++++++++++++++++++++++++++---------
 hw/block/virtio-blk.c           |   30 +++++-
 include/block/aio.h             |   13 +++
 include/block/block.h           |    9 ++
 include/block/coroutine.h       |    7 ++
 include/block/coroutine_int.h   |    5 +
 include/hw/virtio/virtio-blk.h  |   15 +++
 include/qemu/obj_pool.h         |   64 ++++++++++++
 qemu-coroutine-lock.c           |    4 +-
 qemu-coroutine.c                |   33 ++++++
 14 files changed, 553 insertions(+), 105 deletions(-)



[1], http://marc.info/?l=linux-api&m=140486843317107&w=2
[2], http://marc.info/?l=linux-api&m=140418368421229&w=2
[3], http://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git/ #for-3.17/drivers
[4], https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/
[5], http://marc.info/?l=linux-api&m=140377573830230&w=2

Thanks,
--
Ming Lei