Thanks for your reply. > > 1. The fio results so it's clear which cases performed worse and by how > much. > When I set vcpu = 8, read performance is decreased about 25%. In my test, when vcpu = 1, I got a best formance.
> 2. The fio job files. > [testglobal] description=high_iops exec_prerun="echo 3 > /proc/sys/vm/drop_caches" group_reporting=1 rw=read direct=1 ioengine=sync bs=4m numjobs=1 size=2048m > 3. The QEMU command-line to launch the guest. > <domain type='kvm' id='6' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'> <name>vm1</name> <uuid>76d6fca9-904d-1e3e-77c7-67a048be9d60</uuid> <memory unit='KiB'>50331648</memory> <currentMemory unit='KiB'>50331648</currentMemory> <vcpu placement='static'>8</vcpu> <os> <type arch='x86_64' machine='pc-i440fx-1.4'>hvm</type> <boot dev='hd'/> </os> <features> <acpi/> </features> <clock offset='utc'/> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>destroy</on_crash> <devices> <emulator>/usr/bin/qemu-system-x86_64</emulator> <disk type='file' device='disk'> <driver name='qemu' type='raw' cache='none' io='native'/> <source file='/var/lib/libvirt/images/vm1/ubuntu-kvm/tmpJQKe7w.raw'/> <target dev='vda' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </disk> ... <qemu:commandline> <qemu:arg value='-set'/> <qemu:arg value='device.virtio-disk0.scsi=off'/> <qemu:arg value='-set'/> <qemu:arg value='device.virtio-disk0.config-wce=off'/> <qemu:arg value='-set'/> <qemu:arg value='device.virtio-disk0.x-data-plane=on'/> </qemu:commandline> > 4. The host disk configuration (e.g. file systems, local > SATA/FibreChannel/NFS, etc). > -> SSD > 5. The basic host specs including RAM and number of logical CPUs. -> Host : 256GB, CPUs : 31, Guest : 48GB, VCPUs : 8 Thanks. Best Regards. > -----Original Message----- > From: Stefan Hajnoczi [mailto:stefa...@gmail.com] > Sent: Wednesday, September 04, 2013 5:59 PM > To: Jonghwan Choi > Cc: qemu-devel@nongnu.org > Subject: Re: [Qemu-devel] I/O performance degradation with Virtio-Blk- > Data-Plane > > On Mon, Sep 02, 2013 at 05:24:09PM +0900, Jonghwan Choi wrote: > > Nowdays i measured io performance with Virtio-Blk-Data-Plane. > > There was something strange in test. > > When vcpu count is 1, io performance is increased in test > > But vcpu count is over 2, io performance is decreased in test. > > > > i used 3.10.9 stable kernel, qemu(1.4.2) & fio 2.1 > > > > What should i check in my test? > > It's hard to say without any details on your benchmark configuration. > > In general, x-data-plane=on performs well with SMP guests and with > multiple disks. This is because the dataplane threads can process I/O > requests without contending on the QEMU global mutex or the iothread > event loop. > > In order to investigate further, please post: > > 1. The fio results so it's clear which cases performed worse and by how > much. > > 2. The fio job files. > > 3. The QEMU command-line to launch the guest. > > 4. The host disk configuration (e.g. file systems, local > SATA/FibreChannel/NFS, etc). > > 5. The basic host specs including RAM and number of logical CPUs. > > Stefan
