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

Pread

 
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

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