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[Qemu-discuss] mysql and kvm

From: Thomas Manninger
Subject: [Qemu-discuss] mysql and kvm
Date: Sat, 21 Feb 2015 13:02:10 +0100

i have a server with 2x Intel(R) Xeon(R) CPU E5-2660 v3 @ 2.60GHz. I installed debian wheezy with qemu-kvm 2.1+dfsg-9~bpo70+1
I have a mysql database with about 150gb datasize. I installed the same database physical and in a vm.
After same benchmarks, i see, that the vm is in some operations (mysqlimport / export) very slow, some other operations (sqls with many joins), there is not so many different between physical and virtual.
as example: the export on the physical machine needs 37 minutes, in the vm about 55 minutes.
I think, the problem is only at cpu intensive operations.
iostat in the vm during the mysql export (mysql is on a ssd disk):
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
vdb               0.00     0.00  140.00    0.00 17920.00     0.00   256.00     0.02    0.14    0.14    0.00   0.14   2.00
As disk cache, i tried "none" and "writeback", no differnt.
Some idea, how i can get better performance in my vm??

my libvirt config:
<domain type='kvm'>
  <memory unit='KiB'>40960000</memory>
  <currentMemory unit='KiB'>40960000</currentMemory>
  <vcpu placement='static' cpuset="0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38">8</vcpu>
    <type arch='x86_64' machine='pc-i440fx-2.1'>hvm</type>
    <boot dev='hd'/>
    <boot dev='cdrom'/>
  <cpu mode='host-passthrough'></cpu>
  <clock offset='utc'/>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <source dev='/vms/disks/srvmysql1-1'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <source dev='/vms/disks/srvmysql1-datadir1'/>
      <target dev='vdb' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
      <source dev='/vms/disks/srvmysql1-datadir2'/>
      <target dev='vdc' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw' cache='none'/>
      <target dev='hdc' bus='ide'/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    <controller type='usb' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    <interface type='bridge'>
      <mac address='52:54:00:be:28:14'/>
      <source bridge='br-lan'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    <serial type='pty'>
      <target port='0'/>
    <console type='pty'>
      <target type='serial' port='0'/>
    <input type='tablet' bus='usb'/>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <graphics passwd='xxxxx'  type='vnc' port='-1' autoport='yes' listen=''>
      <listen type='address' address=''/>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>

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