[Devel] [PATCH RH9 00/10] vhost-blk: in-kernel accelerator for virtio-blk guests

[Andrey Zhadchenko]

Although QEMU virtio-blk is quite fast, there is still some room for
improvements. Disk latency can be reduced if we handle virito-blk requests
in host kernel so we avoid a lot of syscalls and context switches.
The idea is quite simple - QEMU gives us block device and we translate
any incoming virtio requests into bio and push them into bdev.
The biggest disadvantage of this vhost-blk flavor is raw format.
Luckily Kirill Thai proposed device mapper driver for QCOW2 format to attach
files as block devices: https://www.spinics.net/lists/kernel/msg4292965.html

Also by using kernel modules we can bypass iothread limitation and finaly scale
block requests with cpus for high-performance devices.


There have already been several attempts to write vhost-blk:

Asias' version: https://lkml.org/lkml/2012/12/1/174
Badari's version: https://lwn.net/Articles/379864/
Vitaly's https://lwn.net/Articles/770965/

The main difference between them is API to access backend file. The fastest
one is Asias's version with bio flavor. It is also the most reviewed and
have the most features. So vhost_blk module is partially based on it. Multiple
virtqueue support was addded, some places reworked. Added support for several
vhost workers.

test setup and results:
fio --direct=1 --rw=randread  --bs=4k  --ioengine=libaio --iodepth=128
QEMU drive options: cache=none
filesystem: xfs

SSD:
               | randread, IOPS  | randwrite, IOPS |
Host           |      95.8k      |      85.3k      |
QEMU virtio    |      57.5k      |      79.4k      |
QEMU vhost-blk |      95.6k      |      84.3k      |

RAMDISK (vq == vcpu):
                 | randread, IOPS | randwrite, IOPS |
virtio, 1vcpu    |      123k      |      129k       |
virtio, 2vcpu    |      253k (??) |      250k (??)  |
virtio, 4vcpu    |      158k      |      154k       |
vhost-blk, 1vcpu |      110k      |      113k       |
vhost-blk, 2vcpu |      247k      |      252k       |
vhost-blk, 8vcpu |      497k      |      469k       | *single kernel thread
vhost-blk, 8vcpu |	730k	  |	 701k       | *two kernel threads

https://jira.sw.ru/browse/PSBM-139414
Andrey Zhadchenko (10):
  drivers/vhost: vhost-blk accelerator for virtio-blk guests
  drivers/vhost: use array to store workers
  drivers/vhost: adjust vhost to flush all workers
  drivers/vhost: rework attaching cgroups to be worker aware
  drivers/vhost: rework worker creation
  drivers/vhost: add ioctl to increase the number of workers
  drivers/vhost: assign workers to virtqueues
  drivers/vhost: add API to queue work at virtqueue worker
  drivers/vhost: allow polls to be bound to workers via vqs
  drivers/vhost: queue vhost_blk works at vq workers

 drivers/vhost/Kconfig      |  12 +
 drivers/vhost/Makefile     |   3 +
 drivers/vhost/blk.c        | 830 +++++++++++++++++++++++++++++++++++++
 drivers/vhost/vhost.c      | 253 ++++++++---
 drivers/vhost/vhost.h      |  21 +-
 include/uapi/linux/vhost.h |  14 +
 6 files changed, 1071 insertions(+), 62 deletions(-)
 create mode 100644 drivers/vhost/blk.c

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2.31.1