Hi, if you want to use multiqueues in guest, you need to enabled it on virtio-scsi controller. <controller type='scsi' index='0' model='virtio-scsi' num_queues='8'/> for example. ----- Mail original ----- De: "Vasiliy Tolstov" <v.tolstov(a)selfip.ru&gt; À: "qemu-devel" <qemu-devel(a)nongnu.org&gt;, libvir-list(a)redhat.com Envoyé: Lundi 8 Juin 2015 12:30:59 Objet: [Qemu-devel] poor virtio-scsi performance Hi all! I suspected poor performance of virtio-scsi driver. I did a few tests: Host machine: linux 3.19.1, QEMU emulator version 2.3.0 Guest machine: linux 4.0.4 part of domain xml: <emulator>/usr/bin/kvm</emulator> <disk type='block' device='disk'> <driver name='qemu' type='raw' cache='none' io='native' discard='unmap'/> <source dev='/dev/ram0'/> <backingStore/> <target dev='sda' bus='scsi'/> <alias name='scsi0-0-0-1'/> <address type='drive' controller='0' bus='0' target='0' unit='1'/> </disk> /dev/ram0 I got by running `modprobe brd rd_size=$((5*1024*1024))` on host machine. fio conf: [readtest] blocksize=4k filename=/dev/sdb (/dev/ram0 whe test from host machine) rw=randread direct=1 buffered=0 ioengine=libaio iodepth=32 results: from host: bw=1594.6MB/s, iops=408196, clat=76usec from guest: bw=398MB/s, iops=99720, clat=316usec Both host and guest system I boot with `scsi_mod.use_blk_mq=Y`. Why difference in 4 times?! -- Vasiliy Tolstov, e-mail: v.tolstov(a)selfip.ru