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Performance tuning

2,677 bytes added, 08:42, 26 December 2015
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<translate><!--T:1-->This page describes how to improve the performance of an OpenVZ system.
== HW node environment tuning == <!--T:2-->
=== Disable unnecessary services === <!--T:3-->
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Disable all default services that you do not need to use and then reboot your host.
<!--T:5-->
For example, the <code>audit</code> daemon can significantly decrease performance of linux kernel system calls (up to ~<font color=red>20%</font>) even if you do not use any audit rules, or even if you just stopped this service without host reboot!
 
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To setup default services, use <code>chkconfig</code> or <code>ntsysv</code> in RedHat, or <code>rc-update</code> in Gentoo, <code>update-rc.d</code> on Debian
 
=== Shell scripts performance improvement === <!--T:7-->
 
<!--T:8-->
To improve performance of small shell scripts, which spends a lot of time starting the shell binary itself (like the shell scripts test from the [http://www.tux.org/pub/tux/niemi/unixbench/ unixbench] package), you can set your <code>LANG</code> environment variable to <code>"C"</code>.
 
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To see current settings, type
 
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# locale
For example<!--T:11-->If you want to change it only for the current shell session, do:  <!--T:12--># export LANG=C <!--T:13-->If you want to change the default value, modify the <code>audit/etc/sysconfig/i18n</code> file. <!--T:14-->If your default <code>LANG</code> environment variable was set to something like <code>en_US.UTF-8</code> daemon , you can reduce shell (bash) startup time up to ~<font color=red>15%</font> with <code>LANG=C</code>.  == Container tuning == <!--T:15--> === CPU distribution inside container on SMP hosts === <!--T:16--> <!--T:17-->If the total number of containers in your host is more than CPUs number, and there are many '''threads''' running inside each container it is better to give just a single VCPU to each container.In this case thread memory locality will significantly decrease reduce overhead on SMP memory coherence and overall performance of linux kernel system calls (can be increased up to ~<font color=red>2050-100%</font>) even if you do not ! <!--T:18-->To set the number of CPUs available inside a container, use any audit rules, or even if :  <!--T:19--># vzctl set $CTID --cpus N === Network checksumming === <!--T:20--> <!--T:21-->RHEL 5 based kernel supports IP checksum offload.If network ethernet cards in your host support IP checksum offload then you just stopped can switch this service without host rebootfeature on also for the virtual network devices (venet, veth). <!--T:22-->To check current offload setting for the hardware ethernet card (eth0, for instance) type  <!--T:23--># ethtool -k eth0 Make sure that tx/rx features are switched on.
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To see current offload settings for the venet0 device, type
To setup default services, use <code>chkconfig</code> or <code>ntsysv</code> in RedHat, or <code>rc!--T:25--update</code> in Gentoo, <code>update# ethtool -rc.dv</code> on Debiank venet0
== network checksumming ==<!--T:26-->('''TODO''')To set offload settings on for the venet0 device, type
= Virtual Environment tuning = <!--T:27--># ethtool -K venet0 tx on sg on
== CPU distribution inside VE <!--T:28-->Note, that 'tx on SMP hosts ==/off' enables/disables both tx and rx checksumming features for the all venet devices for all containers and HN.
* If <!--T:29-->The same applies to the total number of VEveth device except that 'tx on/off's enables/disables tx and rx checksumming features for only given virtual ethernet device in your host is more than CPUs number, and there are many tasks running inside each VE, HN and they are scheduled quite often, it's better to give just one CPU for each VEcorresponding container. In this case the VirtualCPU-scheduler overhead can be significantly decreased, and overall performance can be increased up to ~<font color=red>50-100%</font>!
To set the number of CPUs available inside VE use=== Shell scripts performance improvement === <!--T:30-->
<!--T:31-->Please note, that on container creation the default <code>LANG</code> value will be the same as in the HW node. So you can tune it in node (see [[# vzctl Shell scripts performance improvement]] above), or set $VEID --cpus Nit in container the same way.
= Recompiling <!--T:32-->The second important thing is the kernel =locale cache. On <code>rpm</code> based distributions, usually it is created by the <code>glibc-common-XXX.rpm</code> post install script and it can be up to 50 MBytes on some distributions. So on some container templates it can be missed to save disk space. But you can always create it inside container later by the following command (you must be the root user):
== Disable all unnecessary options == <!--T:33--># build-locale-archive
* You can disable all <code!--T:34-->_DEBUG_</code> options And again, in the kernel, this some cases shell (bash) startup time can increase performance be reduced up to ~<font color=red>2015%</font> on some applications.</translate>
* other options ('''TODO''')[[Category: HOWTO]][[Category: Troubleshooting]]