How to determine optimal vCPU for apache

[fletch00]

Hi,

We strictly adhere to the best practice of not over allocating vCPU unless the VM will make use of it (eg Apache, Tomcat)

So in the case of Apache

version 2.2.3

running in Centos5 VM

with 8Gb RAM allocated

Threads (via scoreboard) range from 50-100 active (with max 300)

vSphere ESXi 4.1 (build 260247)

Hardware: Dell R610 with 2 x 6 Core Intel Xeon X5680 CPUS @ 3.3GHz (BTW, why does vCenter report 24 "Logical Processors" - when 2 x 6 = 12?)

how does one best answer the vCPU allocation question?

Is 8 vCPUs (our current setting) better than 4 in this case?

Its my unquantified impression that the overhead of the 8 vCPUs is worth it to serve these 50 - 100 threads.

What have others found or used for decision making rationale for vCPU and apache?

Can vMark benchmark help here?

thanks,

Fletch.

http://vmadmin.info

[fletch00]

Well, I did some benchmarking with apachebench while varying the vCPU's and determined for our configuration the 8 vCPUs were the best:

http://www.vmadmin.info/2011/03/apache-optimal-vcpu-analysis.html

Feedback welcome!

[rickardnobel]

Fletcher Cocquyt wrote:

Hardware: Dell R610 with 2 x 6 Core Intel Xeon X5680 CPUS @ 3.3GHz (BTW, why does vCenter report 24 "Logical Processors" - when 2 x 6 = 12?)

Look for "Hyperthreading enabled", this will give you two logical processors per core, which is why your 12 cores is reported as 24 "logical cpus".