[Xen-users] High Oracle overhead with Xen 4.1.2

[AP <apxeng@xxxxxxxxx>]

I am trying to move a workload from bare metal on to a Xen VM. Prior
to doing that I decided to do some performance benchmarks using
Hammerora (http://hammerora.sourceforge.net/).
The following is the details of the configuration/results of an
experiment to determine the overhead of XEN. The tests were run on the
same hardware. I am seeing a high overhead with Xen. I realize there
will be a IO penalty so I moved all the redo logs in to memory. I do
understand there will be a VM scheduling penalty with Xen but should
it be in the 30-40% range? Does anyone have any insight in to this?

Config 1:
- H/W: 16GB memory, 4 CPU (Intel(R) Xeon(R) CPU E5606  @ 2.13GHz)
- Host OS: Ubuntu 11.04 (Linux 3.0.0) with XEN 4.1.2
- Guest OS: CentOS 5.6 (Linux 2.6.18-238.el5) with 12 GB memory and 4 vcpus
- Guest Software: HammerOra 2.9 (Load Testing Tool) against Oracle 11.2.0.1.0
- Setup:
  a) Dom 0 running 4 vcpus
  b) 1 Guest running Oracle 11.2.0.1.0 with 12 GB memory and 4 vcpus
  c) 1 Guest running HammerOra 2.9 with 1 GB memory and 2 vcpus
  Note 1: None of the vcpus are pinned.
  Note 2: The Oracle cache size is sufficiently large and the redo
logs are in memory (tmpfs) so there is negligible I/O (confirmed via
AWR reports)
- Result:
  1 vusers: Oracle Txns/minute: 26769
  2 vusers: Oracle Txns/minute: 47878

Config 2:
- H/W: 12 GB memory (memory was reduced using the kernel command
line),  4 CPU (Intel(R) Xeon(R) CPU E5606  @ 2.13GHz)
- OS: CentOS 5.6 (Linux 2.6.18-238.el5)
- Software: HammerOra 2.9 (Load Testing Tool) against Oracle 11.2.0.1.0
- Note 1: The Oracle cache size is sufficiently large and the redo
logs are in memory (tmpfs) so there is negligible I/O (confirmed via
AWR reports)
- Result:
  1 vusers: Oracle Txns/minute: 39840
  2 vusers: Oracle Txns/minute: 77423

Result:
- 1 vuser: 33% overhead due to XEN
- 2 vuser: 39% overhead due to XEN

Thanks,
AP

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