Hello.
I have been doing some performance tests with Xen and CentOS and have found some strange statistics when comparing the virtual memory (/proc/vmstat) and I/O (/proc/diskstat) statistics between the Domain 0 and guests.
When I look at the "pgpgin" statistic it is exactly the same as the "read sectors" in Dom0. However, when I look at the same statistics in the guest, the "read sectors" is exactly 2x "pgpgin".
I have tried this on 2 different versions, each on a different physical server. Here is an example of the statistics over a 30 second period (while running a benchmark in Dom1) in the Dom0 and Guest Domain.
pgpgin read sectors
======= =========
Dom0 1698024 1698024
Dom1 848412 1696824
I have looked at some various settings to see if I could explain it. I can't tell if the Dom1 guest kernel is reporting incorrectly, or there is some other explanation. If anyone has any ideas about this I would appreciate any feedback.
Dom 0 kernels
3.10.29-11.el6.centos.alt.x86_64
3.4.54-8.el6.centos.alt.x86_64
Guest kernel
2.6.32-431.el6.x86_64
Thanks,
Deron
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