[libvirt-users] data monitored by "virDomainBlockStats" API not consistent with ones reading from /proc/[pid]/io, and corrugated with /proc/diskstats
Eric Blake
eblake at redhat.com
Wed Jun 25 18:50:50 UTC 2014
On 06/25/2014 05:11 AM, coperd wrote:
[please don't top-post on technical lists]
> Command line "virsh domblkstat $vmname vda” get the results below:
> vda rd_bytes 639415808
> vda wr_bytes 728186880
>
> Command line "cat /proc/4438/io” get the result below:
> read_bytes: 772415488
> write_bytes: 734040064
Bear in mind that for some file formats, such as qcow2, qemu must read
(and write) additional I/O to manage the metadata of the file in
comparison to the amount of read and writes performed on behalf of the
guest; the qemu numbers are reported from the guest perspective, not
what qemu asked the host kernel to do. So seeing /proc/NN/io have
larger numbers than qemu makes total sense.
I'm still not clear how you are getting vcpu PID numbers for reading
from /proc; it's not something that libvirt is currently advertising.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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