libvirt users - Feb 2013 - The accurate CPU usage of a domain?

Hi,all
I want to get a relatively accurate cpu usage of a domain. I have a few
questions about  virDomainGetInfo:  struct virDomainInfo{  unsigned char state :
//the running state, one of virDomainState    unsigned long maxMem :// the
maximum memory in KBytes allowed   unsigned long memory :// the memory in KBytes
used by the domain   unsigned short nrVirtCpu :// the number of virtual CPUs for
the domain   unsigned long long cpuTime : //the CPU time used in nanoseconds   }
If a domain is assigned to 4 vcpus and my machine has 6 physical cores, then the
cpuTime in virDomainInfo should be the sum of cpu time of the 4 vcpus. When I
want to calculate the cpu usage, which of the following is more accurate?     
1/4 * cpu time /  total time  or  4/6 * cpu time / total time  or just cpu time
/ total time

regardszhangzhang

 		 	   		  
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On 02/27/2013 08:25 PM, ?? wrote:
> 
> Hi,all
> I want to get a relatively accurate cpu usage of a domain. I have a few
questions about  virDomainGetInfo:  struct virDomainInfo{  unsigned char state :
//the running state, one of virDomainState    unsigned long maxMem :// the
maximum memory in KBytes allowed   unsigned long memory :// the memory in KBytes
used by the domain   unsigned short nrVirtCpu :// the number of virtual CPUs for
the domain   unsigned long long cpuTime : //the CPU time used in nanoseconds   }
> If a domain is assigned to 4 vcpus and my machine has 6 physical cores,
then the cpuTime in virDomainInfo should be the sum of cpu time of the 4 vcpus.
When I want to calculate the cpu usage, which of the following is more accurate?
1/4 * cpu time /  total time  or  4/6 * cpu time / total time  or just cpu time
/ total time
[Can you please convince your mailer to wrap long lines, and use proper
line breaks when quoting code, so that your mail is legible?]

At this point, I'd suggest the best way of knowing what times are
returned is checking the source code; but patches to make the
documentation more obvious for the next person would be appreciated.

If you want more statistics, which might provide you with more accuracy,
you might also be interested in looking at the virDomainGetCPUStats.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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