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. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Peter Booth
2009-Apr-01 20:19 UTC
Re: [Xen-users] very interesting Xen Disk I/O performance
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. > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users