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KVM虚拟机CPU开销高性能优化例子 - 配置CPU flag

3 minute read

背景

在装好后, 发现一个问题, 即使我的虚拟机上没跑任何用户进程, 在宿主机上对应的qemu-kvm进程的CPU利用率也有9.0左右.

本文将要介绍一下优化的方法，主要是精简配置，以及设置对应的CPU FLAG。

优化过程

删掉一些不必要的控制器(如USB), 然后添加CPU模块, 使用本地CPU的flag.

virsh # shutdown centos6_6_x64  
virsh # edit centos6_6_x64  
..................

原来的配置文件大概是这样的,

<domain type='kvm' id='2'>  
  <name>centos6_6_x64</name>  
  <uuid>4c613d4e-716b-f2cb-4df3-09bc7779f7df</uuid>  
  <memory unit='KiB'>4194304</memory>  
  <currentMemory unit='KiB'>4194304</currentMemory>  
  <vcpu placement='static'>4</vcpu>  
  <os>  
    <type arch='x86_64' machine='rhel6.6.0'>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/libexec/qemu-kvm</emulator>  
    <disk type='file' device='disk'>  
      <driver name='qemu' type='raw' cache='writethrough'/>  
      <source file='/data02/kvmdisk/disk01.img'/>  
      <target dev='vda' bus='virtio'/>  
      <alias name='virtio-disk0'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' 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' model='ich9-ehci1'>  
      <alias name='usb0'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x7'/>  
    </controller>  
    <controller type='usb' index='0' model='ich9-uhci1'>  
      <alias name='usb0'/>  
      <master startport='0'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0' multifunction='on'/>  
    </controller>  
    <controller type='usb' index='0' model='ich9-uhci2'>  
      <alias name='usb0'/>  
      <master startport='2'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x1'/>  
    </controller>  
    <controller type='usb' index='0' model='ich9-uhci3'>  
      <alias name='usb0'/>  
      <master startport='4'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x2'/>  
    </controller>  
    <controller type='ide' index='0'>  
      <alias name='ide0'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>  
    </controller>  
    <interface type='bridge'>  
      <mac address='52:54:00:76:ac:2b'/>  
      <source bridge='virbr0'/>  
      <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/2'/>  
      <target port='0'/>  
      <alias name='serial0'/>  
    </serial>  
    <console type='pty' tty='/dev/pts/2'>  
      <source path='/dev/pts/2'/>  
      <target type='serial' port='0'/>  
      <alias name='serial0'/>  
    </console>  
    <input type='tablet' bus='usb'>  
      <alias name='input0'/>  
    </input>  
    <memballoon model='virtio'>  
      <alias name='balloon0'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>  
    </memballoon>  
  </devices>  
</domain>

修改后的XML如下, CPU使用host-model=allow :

virsh # dumpxml centos6_6_x64  
<domain type='kvm'>  
  <name>centos6_6_x64</name>  
  <uuid>4c613d4e-716b-f2cb-4df3-09bc7779f7df</uuid>  
  <memory unit='KiB'>4194304</memory>  
  <currentMemory unit='KiB'>4194304</currentMemory>  
  <vcpu placement='static'>4</vcpu>  
  <os>  
    <type arch='x86_64' machine='rhel6.6.0'>hvm</type>  
    <boot dev='hd'/>  
  </os>  
  <features>  
    <acpi/>  
    <apic/>  
  </features>  
  <cpu mode='host-model'>  
    <model fallback='allow'/>  
  </cpu>  
  <clock offset='utc'/>  
  <on_poweroff>destroy</on_poweroff>  
  <on_reboot>restart</on_reboot>  
  <on_crash>restart</on_crash>  
  <devices>  
    <emulator>/usr/libexec/qemu-kvm</emulator>  
    <disk type='file' device='disk'>  
      <driver name='qemu' type='raw' cache='writethrough'/>  
      <source file='/data03/kvmdisk/disk01.img'/>  
      <target dev='vda' bus='virtio'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>  
    </disk>  
    <controller type='usb' index='0'>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>  
    </controller>  
    <interface type='bridge'>  
      <mac address='52:54:00:76:ac:2b'/>  
      <source bridge='virbr0'/>  
      <model type='virtio'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>  
    </interface>  
    <serial type='pty'>  
      <target port='0'/>  
    </serial>  
    <console type='pty'>  
      <target type='serial' port='0'/>  
    </console>  
    <memballoon model='virtio'>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>  
    </memballoon>  
  </devices>  
</domain>

开机

virsh # start centos6_6_x64  
Domain centos6_6_x64 started  
  
virsh # console centos6_6_x64  
Connected to domain centos6_6_x64  
Escape character is ^]

查看当前虚拟机启动时配置的cpu flag, 判断为Nehalem:

[root@db-172-16-3-150 ~]# ps -ewf|grep kvm  
root       966     2  0 Apr01 ?        00:00:00 [kvm-irqfd-clean]  
qemu     20418     1 31 10:18 ?        00:00:16 /usr/libexec/qemu-kvm -name centos6_6_x64 -S -M rhel6.6.0 -cpu Nehalem,+rdtscp,+dca,+pdcm,+xtpr,+tm2,+est,+vmx,+ds_cpl,+monitor,+dtes64,+pbe,+tm,+ht,+ss,+acpi,+ds,+vme -enable-kvm -m 4096 -realtime mlock=off -smp 4,sockets=4,cores=1,threads=1 -uuid 4c613d4e-716b-f2cb-4df3-09bc7779f7df -nographic -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/centos6_6_x64.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/data03/kvmdisk/disk01.img,if=none,id=drive-virtio-disk0,format=raw,cache=writethrough -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=26 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:76:ac:2b,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -msg timestamp=on

现在qemu-kvm CPU使用率降低到0.x%

XML配置文件样本,

[root@db-172-16-3-150 ~]# cd /usr/share/libvirt/  
[root@db-172-16-3-150 libvirt]# ll -R  
.:  
total 28K  
-rw-r--r--. 1 root root  19K Jan 29 20:49 cpu_map.xml  
drwxr-xr-x. 2 root root 4.0K Apr  1 13:33 networks  
drwxr-xr-x. 2 root root 4.0K Feb 11 10:42 schemas  
  
./networks:  
total 4.0K  
-rw-r--r--. 1 root root 230 Jan 29 20:49 default.xml  
  
./schemas:  
total 236K  
-rw-r--r--. 1 root root 7.4K Jan 29 20:49 basictypes.rng  
-rw-r--r--. 1 root root 8.7K Jan 29 20:49 capability.rng  
-rw-r--r--. 1 root root 101K Jan 29 20:49 domaincommon.rng  
-rw-r--r--. 1 root root  285 Jan 29 20:49 domain.rng  
-rw-r--r--. 1 root root 3.9K Jan 29 20:49 domainsnapshot.rng  
-rw-r--r--. 1 root root  12K Jan 29 20:49 interface.rng  
-rw-r--r--. 1 root root 5.8K Jan 29 20:49 networkcommon.rng  
-rw-r--r--. 1 root root  11K Jan 29 20:49 network.rng  
-rw-r--r--. 1 root root 8.8K Jan 29 20:49 nodedev.rng  
-rw-r--r--. 1 root root  30K Jan 29 20:49 nwfilter.rng  
-rw-r--r--. 1 root root 1.6K Jan 29 20:49 secret.rng  
-rw-r--r--. 1 root root  788 Jan 29 20:49 storageencryption.rng  
-rw-r--r--. 1 root root  12K Jan 29 20:49 storagepool.rng  
-rw-r--r--. 1 root root 4.9K Jan 29 20:49 storagevol.rng

还记得cluster.rng吗?都是类似的模板哦。

[root@db-172-16-3-150 libvirt]# cd /usr/share/cluster/  
[root@db-172-16-3-150 cluster]# ll  
total 20K  
-rwxr-xr-x. 1 root root 2.4K Oct 15 19:45 checkquorum  
-rw-r--r--. 1 root root 2.4K Oct 15 19:45 checkquorum.wdmd  
lrwxrwxrwx. 1 root root   28 Feb 11 10:42 cluster.rng -> /var/lib/cluster/cluster.rng

参考

其他优化手段参考如下 :

1. http://www.linux-kvm.org/page/Tuning_KVM
2. http://wiki.qemu.org/Qemu-doc.html
3. https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Virtualization_Tuning_and_Optimization_Guide/index.html
4. /usr/share/libvirt

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