[v2] block: vhost-blk backend

[RFC PATCH v2 0/1] block: vhost-blk backend

Andrey Zhadchenko via posted 1 patch 1 year, 6 months ago

Diff against v1
Download series mbox

Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20221013203130.690327-1-andrey.zhadchenko@virtuozzo.com

Maintainers: Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

hw/block/Kconfig              |   5 +
hw/block/meson.build          |   4 +
hw/block/vhost-blk.c          | 403 ++++++++++++++++++++++++++++++++++
hw/virtio/meson.build         |   3 +
hw/virtio/vhost-blk-pci.c     | 102 +++++++++
include/hw/virtio/vhost-blk.h |  52 +++++
meson.build                   |   6 +
meson_options.txt             |   2 +
scripts/meson-buildoptions.sh |   3 +
9 files changed, 580 insertions(+)
create mode 100644 hw/block/vhost-blk.c
create mode 100644 hw/virtio/vhost-blk-pci.c
create mode 100644 include/hw/virtio/vhost-blk.h

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[RFC PATCH v2 0/1] block: vhost-blk backend

Posted by Andrey Zhadchenko via 1 year, 6 months ago

Sending second version of this patchset as @stefanha requested.
The main difference from the previous version is added vhost
multithreading support.

Also I must note currently there are several problems which
I intend to reconsider/fix later:
 - vmsd is present but migration is not supported
 - BlockConf is used but block layer is actually bypassed
 - posix BlockDriver internal state guessing

---

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 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. This is planned to be
implemented in next version.

Linux kernel module part:
v2: https://lore.kernel.org/kvm/20221013151839.689700-1-andrey.zhadchenko@virtuozzo.com/

test setups and results:
fio --direct=1 --rw=randread  --bs=4k  --ioengine=libaio --iodepth=128
QEMU options: cache=none, iothread, aio=threads
filesystem: xfs

SSD:
               | randread, IOPS  | randwrite, IOPS |
Host           |      95.8k	 |	85.3k	   |
QEMU virtio    |      61.5k	 |	79.9k	   |
QEMU vhost-blk |      95.6k	 |	84.3k	   |

RAMDISK (vq == vcpu == numjobs):
                 | randread, IOPS | randwrite, IOPS |
virtio, 1vcpu    |	133k	  |	 133k       |
virtio, 2vcpu    |	305k      |	 306k       |
virtio, 4vcpu    |	310k	  |	 298k       |
virtio, 8vcpu    |	271k      |	 252k       |
vhost-blk, 1vcpu |	110k	  |	 113k       |
vhost-blk, 2vcpu |	247k	  |	 252k       |
vhost-blk, 4vcpu |	558k	  |	 556k       |
vhost-blk, 8vcpu |	576k	  |	 575k       | *single kernel thread
vhost-blk, 8vcpu |      803k      |      779k       | *two kernel threads

Andrey Zhadchenko (1):
  block: add vhost-blk backend

 hw/block/Kconfig              |   5 +
 hw/block/meson.build          |   4 +
 hw/block/vhost-blk.c          | 403 ++++++++++++++++++++++++++++++++++
 hw/virtio/meson.build         |   3 +
 hw/virtio/vhost-blk-pci.c     | 102 +++++++++
 include/hw/virtio/vhost-blk.h |  52 +++++
 meson.build                   |   6 +
 meson_options.txt             |   2 +
 scripts/meson-buildoptions.sh |   3 +
 9 files changed, 580 insertions(+)
 create mode 100644 hw/block/vhost-blk.c
 create mode 100644 hw/virtio/vhost-blk-pci.c
 create mode 100644 include/hw/virtio/vhost-blk.h

-- 
2.31.1