Hi,
With QEMU x-data-plane, I find the performance has not been improved
very much. Please see following two settings.
Setting 1: I/O thread in host OS (VMM) reads 4KB each time from disk
(8GB in total). Pin the I/O thread to pCPU 5 which will serve I/O
thread dedicatedly. I find the performance is around 250 MB/s.
Setting 2: I/O thread in guest OS (VMM) reads 4KB each time from
virtual disk (8GB in total). Pin the I/O thread to vCPU 5 and pin vCPU
5 thread to pCPU5 so that vCPU 5 handles this I/O thread dedicatedly
and pCPU5 serve vCPU5 dedicatedly. In order to keep vCPU5 not to be
idle, I also pin one cpu intensive thread (while (1) {i++}) on vCPU 5
so that the I/O thread on it can be served without delay. For this
setting, I find the performance for this I/O thread is around 190
MB/s.
NOTE: For setting 2, I also pin the QEMU dedicated IOthread
(x-data-plane) in host OS to pCPU to handle I/O requests from guest OS
dedicatedly.
I think for setting 2, the performance of I/O thread should be almost
the same as setting 1. I cannot understand why it is 60 MB/s lower
than setting 1. I am wondering whether there are something wrong with
my x-data-plane setting or virtio setting for VM. Would you please
give me some hints? Thank you.
Libvirt version: 2.4.0
QEMU version: 2.3.0
The libvirt xml configuration file is like following (I only start
one VM with following xml config).
<domain type='kvm' id='1'
xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
<name>vm</name>
<uuid>3290a8d0-9d9f-b2c4-dd46-5d0d8a730cd6</uuid>
<memory unit='KiB'>8290304</memory>
<currentMemory unit='KiB'>8290304</currentMemory>
<vcpu placement='static'>15</vcpu>
<cputune>
<vcpupin vcpu='0' cpuset='0'/>
<vcpupin vcpu='1' cpuset='1'/>
<vcpupin vcpu='2' cpuset='2'/>
<vcpupin vcpu='3' cpuset='3'/>
<vcpupin vcpu='4' cpuset='4'/>
<vcpupin vcpu='5' cpuset='5'/>
<vcpupin vcpu='6' cpuset='6'/>
<vcpupin vcpu='7' cpuset='7'/>
<vcpupin vcpu='8' cpuset='8'/>
<vcpupin vcpu='9' cpuset='9'/>
<vcpupin vcpu='10' cpuset='10'/>
<vcpupin vcpu='11' cpuset='11'/>
<vcpupin vcpu='12' cpuset='12'/>
<vcpupin vcpu='13' cpuset='13'/>
<vcpupin vcpu='14' cpuset='14'/>
</cputune>
<resource>
<partition>/machine</partition>
</resource>
<os>
<type arch='x86_64' machine='pc-i440fx-2.2'>hvm</type>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
<pae/>
</features>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<emulator>/usr/bin/kvm-spice</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='raw' cache='none' io='native'/>
<source file='/var/lib/libvirt/images/vm.img'/>
<target dev='vda' bus='virtio'/>
<alias name='virtio-disk0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06'
function='0x0'/>
</disk>
<disk type='block' device='cdrom'>
<driver name='qemu' type='raw'/>
<target dev='hdc' bus='ide'/>
<readonly/>
<alias name='ide0-1-0'/>
<address type='drive' controller='0' bus='1' target='0' unit='0'/>
</disk>
<controller type='usb' index='0'>
<alias name='usb0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01'
function='0x2'/>
</controller>
<controller type='pci' index='0' model='pci-root'>
<alias name='pci.0'/>
</controller>
<controller type='ide' index='0'>
<alias name='ide0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01'
function='0x1'/>
</controller>
<controller type='scsi' index='0'>
<alias name='scsi0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>
</controller>
<interface type='network'>
<mac address='52:54:00:8e:3d:06'/>
<source network='default'/>
<target dev='vnet0'/>
<model type='virtio'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03'
function='0x0'/>
</interface>
<serial type='pty'>
<source path='/dev/pts/8'/>
<target port='0'/>
<alias name='serial0'/>
</serial>
<console type='pty' tty='/dev/pts/8'>
<source path='/dev/pts/8'/>
<target type='serial' port='0'/>
<alias name='serial0'/>
</console>
<input type='mouse' bus='ps2'/>
<input type='keyboard' bus='ps2'/>
<graphics type='vnc' port='5900' autoport='yes' listen='127.0.0.1'>
<listen type='address' address='127.0.0.1'/>
</graphics>
<video>
<model type='cirrus' vram='9216' heads='1'/>
<alias name='video0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02'
function='0x0'/>
</video>
<memballoon model='virtio'>
<alias name='balloon0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x05'
function='0x0'/>
</memballoon>
</devices>
<seclabel type='none'/>
<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>
</domain>
Thank you,
Weiwei Jia
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