You have eight cores and two VMs with 2vcpu. Can you try the
experiment with 8 VMs?
On Mar 31, 2009, at 12:02 AM, Jia Rao wrote:
Hi all,
I tested the xen vm disk I/O this weekend and had some interesting
observations:
I ran TPC-C benchmarks (mostly random small disk read) within two
VMs (PV) with the exactly the same resource and software
configuration. I started the benchmarks in the two VMs at the same
time (started with a script, the time difference is within several
ms). The Xen VM scheduler seems always favor one VM, which results
in a 50% better performance over the other VM. I changed the
seqence of the VM creation and application starting order, the
specific VM always got better performance, 30%-50% better.
What could be the reason that xen always favor a specific VM?
I ran the above test for several more times. Between each run, I
purged the cached data within each VM to make the I/O demand always
the same. It is interesting that the performance gap between the two
VM becomes smaller and smaller. After 6 runs, the performance almost
the same.
Anyone has any idea? Does the VM scheduler scheduling VMs based on
history?
I am using Xen 3.3.1, CentOS 5.1, linux 2.8.18-x86_64
Each VM has 512M, 2-VCPU not pinned. Dom0 with 512M, not pinned.
Host: dell poweredge 1950: 8G, two quad-core Intel xeon.
Thanks in advance,
Jia.
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