Hi All
We are currently testing our product using KVM as the hypervisor.
We are not using KVM as a bare-metal hypervisor. We use it on top
of a RHEL installation. So basically RHEL acts as our host and
using KVM we deploy guests on this system.
We have all along tested and shipped our application image for
VMware ESXi installations , So this it the first time we are
trying our application image on a KVM hypervisor.
On this front i have done some tests to find out how our
application's response time is when deployed on KVM and then
compare it with a VM deployed on VMware ESXi. We have a benchmark
test that basically loads the application simulating a load of 100
parallel users logging into the system and downloading reports.
These tests basically use a HTTP GET query to load the application
VM. In addition to that i have taken care to use the same hardware
for both the tests , one with RHEL(Host)+KVM and another with
VMware ESXi. All the hardware specifications for both the servers
remain the same. The load test also remains the same for testing
with both the servers.
First observation is that the average response time on the VMware
ESXi is : 500 milli-seconds while the application's average
response time when deployed using RHEL(Host)+ KVM is : 1050
milli-seconds. The response time of the application when deployed
on KVM is twice as much as when it is deployed using VMware ESXi.
I did few more tests to find which sub-system on these servers
shows varying metrics.
First i started with IOZone to find out if there is any mismatch
in the speed with which data is read / written to the local disk
on the two VMs and found that "Read" speed in the VM that was
deployed using RHEL(Host)+KVM was twice as slow as the VM which
was deployed using VMware ESXi.
For more on IoZone , Please refer : http://www.iozone.org/
more specifically the following IoZone metrics were twice as less
when compared to the server running with VMware ESXi:
| Read |
| Re-read |
| Reverse-Read |
| Stride Read |
Note: I had run the IoZone tests on the VMs on both the servers.
Second observation to be made was the output from the "top"
command. I could see that the VM deployed on RHEL(Host)+KVM was
showing high numbers for the following metrics when compared with
the VM deployed on VMware ESXi:
load averages
%sy for all the logical processors
%si for all the logical processors
i debugged further to find out which device is causing more
interrupts and found it to be "ide0" , See the output from the
/proc/interrupts file below:
The other interrupts apart from ide0 are pretty much similar to
the VM deployed using VMware ESXi.
************/proc/interrupts *******************
[root@localhost ~]# cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3 CPU4
CPU5 CPU6 CPU7
0: 795827 0 0 0
0 0 0 0 IO-APIC-edge timer
1: 65 0 0 0
0 0 0 0 IO-APIC-edge i8042
6: 2 0 0 0
0 0 0 0 IO-APIC-edge floppy
8: 0 0 0 0
0 0 0 0 IO-APIC-edge rtc
9: 0 0 0 0
0 0 0 0 IO-APIC-level acpi
10: 425785 0 0 0
0 0 0 0 IO-APIC-level virtio0, eth0
11: 47 0 0 0
0 0 0 0 IO-APIC-level uhci_hcd:usb1,
HDA Intel
12: 730 0 0 0
0 0 0 0 IO-APIC-edge i8042
14: 188086 0 0 0
0 0 0 0 IO-APIC-edge ide0
NMI: 0 0 0 0
0 0 0 0
LOC: 795813 795798 795783 795767 795752
795737 795723 795709
ERR: 0
MIS: 0
*********************************************
Any pointers to improving the response time for the VM for
RHEL(Host)+KVM installation would be greatly appreciated.
Thanks
Jatin