Re: What does cpu_time returned by virDomainGetCPUStats mean?
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在 2012年4月17日 上午4:11，Eric Blake <eblake@xxxxxxxxxx> 写道： > On 04/16/2012 05:37 AM, Zhihua Che wrote: >> >> I thought this value store the run time of the cpu since last boot. > > The intent is to store run time of the hypervisor process managing the > guest (which therefore is larger than the amount of time that the guest > thinks it has been running, since the hypervisor has some overhead). > But the API is flexible enough that we can add more statistics, if it > proves easy to collect such additional statistics. > >> But I find I was wrong because this value would increase until it >> wraps down and doesn't reset even the domain is restarted. > > How are you restarting the guest? If it is by rebooting the guest > _within the same qemu process_, then no, the numbers won't reset. Based > on how the cpuacct cgroup works, the numbers should only wrap when you > actually create a new qemu process (actually stop the guest and boot it > fresh in a new qemu process, rather than rebooting the guest within the > same qemu process). After reading your post, I did the below experiment again. I started the domain by issuing 'start ubuntu-1' and shutted down my domain by issuing 'destroy ubuntu-1'. (BTW, I cannot shutdown my domain by 'shutdown ubunut-1'. I guess my domain image got something wrong. I wish this didn't affect the experiment) Here are my two sample values. start ubunt-1 cpu0+cpu1 11239925290 cpu0 6034491893 cpu1 5205433307 destroy and start ubunu-1 cpu0+cpu1 10621566430 cpu0 5403373809 cpu1 5218192621 I can't determine whether these value reseted because total number is lower than that before restarting while one cpu is larger or lower. These values really confuse me. I check the kvm process id through ps. I'm sure the two running domain are assigned two different process id. I guess that means they run as different qemu process as you mentioned. > > Perhaps we should be improving our XML to track delta usage since a > given point in time, and when we detect a domain reboot, update that > delta point so that the usage will again appear to be 0; allowing a > delta calculation would also let us "track" CPU usage even across domain > migration or managedsave/restore. > >> >> So, what does this value mean? >> >> How can I get the CPU usage of the domain? >> >> I found nothing on the API reference doc page:-(. No word is >> related with the meaning of the returned array of virTypedParameter by >> virDomainGetCPUStats(). > > I found this: > > http://libvirt.org/html/libvirt-libvirt.html#VIR_DOMAIN_CPU_STATS_CPUTIME > > "cpu usage in nanoseconds, as a ullong" > > and looking at libvirt.h, VIR_DOMAIN_CPU_STATS_CPUTIME maps to the > "cpu_time" name of your API call. > > If that still isn't enough information, could you help out by submitting > patches to improve our documentation? > > -- > Eric Blake eblake@xxxxxxxxxx +1-919-301-3266 > Libvirt virtualization library http://libvirt.org > _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
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