[libvirt-users] problem when get the vm cpu stat

[Michal Privoznik]

On 19.04.2013 09:40, Wangkai (Kevin,C) wrote:
> Hi all,
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> 
> I try to get vm cpu stat by function “virDomainGetCPUStats”,  when the vm
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> Cpu usage is 100%, I can see from the vm shell by “top”,  when the info
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> Get by the “virDomainGetCPUStats” show only the “cpu_time” increased,
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> “user_time” and “system_time” was not changed at all.
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> Is that correct ? How can I get the vm cpu usage?
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> nparams = virDomainGetCPUStats(domain, NULL, 0, -1, 1, 0);
> 
> virDomainGetCPUStats(domain, params, nparams, -1, 1, 0);

You can gather statistics in similar way that 'top' does. Query current
usage in loops and divide increment by time. Something like:


nparams = virDomainGetCPUStats(domain, NULL, 0, -1, 1, 0);

while (1) {
  struct timeval now, then;
  int i, j;

  gettimeofday(&now, NULL);
  virDomainGetCPUStats(domain, params_now, nparams, -1, 1, 0);

  /* some sleep, e.g. 500ms */
  usleep(5000);

  virDomainGetCPUStats(domain, params_then, nparams, -1, 1, 0);
  gettimeofday(&then, NULL);

  /* find appropriate i and j */

  /* virDomainGetCPUStats is returning time in microseconds IIRC */
  float usage_in_percent = (params_then[i] - params_now[j]) /
(then.tv_usec - now.tv_usec) / 1000;

  printf("%f\n", usage_in_percent);
}