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 v2: patch 1/10 - removed unused VHOST_BLK_VQ - reworked bio handling a bit: now add all pages from signle iov into single bio istead of allocating one bio per page - changed how to calculate sector incrementation - check move_iovec() in vhost_blk_req_handle() - remove snprintf check and better check ret from copy_to_iter for VIRTIO_BLK_ID_BYTES requests - discard vq request if vhost_blk_req_handle() returned negative code - forbid to change nonzero backend in vhost_blk_set_backend(). First of all, QEMU sets backend only once. Also if we want to change backend when we already running requests we need to be much more careful in vhost_blk_handle_guest_kick() as it is not taking any references. If userspace want to change backend that bad it can always reset device. - removed EXPERIMENTAL from Kconfig patch 3/10 - don't bother with checking dev->workers[0].worker since dev->nworkers will always contain 0 in this case patch 6/10 - Make code do what docs suggest. Previously ioctl-supplied new number of workers were treated like an amount that should be added. Use new number as a ceiling instead and add workers up to that number. v3: patch 1/10 - reworked bio handling a bit - now create new only if the previous is full patch 2/10 - set vq->worker = NULL in vhost_vq_reset() 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 | 827 +++++++++++++++++++++++++++++++++++++ drivers/vhost/vhost.c | 253 +++++++++--- drivers/vhost/vhost.h | 21 +- include/uapi/linux/vhost.h | 14 + 6 files changed, 1068 insertions(+), 62 deletions(-) create mode 100644 drivers/vhost/blk.c -- 2.31.1 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel
