As there is some interest from QEMU userspace, I am sending second version of this patchet. Main addition is a few patches about vhost multithreading so vhost-blk can be scaled. Generally the idea is not a new one - somehow attach workers to the virtqueues and do the work on them. I have seen several previous attemps like cgroup-aware worker pools or the userspace threads, but they seem very complicated and involve a lot of subsystems. Probably just spawning a few more vhost threads can do a good job. As this is RFC, I did not convert any vhost users except vhost_blk. If anyone is interested in this regarding other modules, please tell me. I can test it to see if it is beneficial and maybe send multithreading separately. Also multithreading part may eventually be of help with vdpa-blk. --- 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 | 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 v2: Re-measured virtio performance with aio=threads and iothread on latest QEMU vhost-blk changes: - removed unused VHOST_BLK_VQ - reworked bio handling a bit: now add all pages from signle iov into bio until it is full 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 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 cgroups attachment 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's 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 | 819 +++++++++++++++++++++++++++++++++++++ drivers/vhost/vhost.c | 263 +++++++++--- drivers/vhost/vhost.h | 21 +- include/uapi/linux/vhost.h | 13 + 6 files changed, 1064 insertions(+), 67 deletions(-) create mode 100644 drivers/vhost/blk.c -- 2.31.1
