Article ID: 122109, created on Jun 20, 2014, last review on Jun 20, 2014

  • Applies to:
  • Virtuozzo 6.0
  • Virtuozzo hypervisor

Symptoms

While Virtual Machine shows idle CPU Usage on the inside, it might be consuming up to 500-900% on the Hardware Node side.

Example:

On a Hardware Node side prl_vm_app process shows 900% CPU usage:

    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 830946 root      20   0  133g  20g  22m S 900.6  8.1  66150:19 prl_vm_app

Meanwhile, inside of the Virtual Machine usage is relatively low:

    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  33265 27        20   0 1543m 388m 4388 S 111.6  1.9  10723:14 mysqld
 434182 apache    20   0  363m  17m 4900 S 13.7  0.1   0:02.78 httpd
 434180 apache    20   0  372m  27m 4940 S 10.1  0.1   0:02.87 httpd
 436199 10000     20   0  224m  19m 8340 S  4.6  0.1   0:00.88 php-cgi
 421404 apache    20   0  423m  30m 7160 S  3.9  0.2   0:28.92 httpd
 866148 27        20   0  611m 125m 6152 S  3.6  0.6 766:05.10 mysqld
  24693 root      20   0  328m 3148  664 S  2.9  0.0  96:48.57 sw-collectd
 436273 root      20   0 15964 2300 1000 R  1.6  0.0   0:00.22 top
     52 root      20   0     0    0    0 S  1.0  0.0  83:24.09 events/9
     43 root      20   0     0    0    0 S  0.7  0.0  64:54.24 events/0

Cause

This behavior is caused by specific optimization which is enabled only when Virtual Machine is almost idle, it's called "adaptive hltdelay". It tries to reduce number of context switches, but causes extra cycles in VM Monitor (prl_vm_app process), therefore process shows high CPU utilization.

Once Virtual Machine will get any load "adaptive hltdelay" optimization will be disabled, and you will not observe any extra load on the Hardware Node side.

Resolution

This behavior will not cause any performance problems when Virtual Machines gets workload, it is safe to ignore it.

Search Words

High cpu usage on HW node, not in VM

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