High CPU Usage for PHP and MySQL on VPS

[Bestrafung]

I have a cPanel VPS setup on CentOS 5.10 running under Hyper-V (Windows Server 2008 R2). Everything was running fine until recently when we installed a chat addon to a client's vBulletin forums. Anytime the chat addon is used the server load skyrockets. While looking into this I see that we are getting a large amount of CPU usage in general for PHP and MySQL. I have confirmed it's not a memory or swap issue. Does anyone have any ideas what could be causing the high usage or how to reduce it?

Here's some of the information from WHM's top processes:
User Domain % CPU Process
user1 user1.com 48.0

 <defunct>
user1 	user1.com 	47.0  		[php] <defunct>
user2 	user2.com 	46.0  		[php] <defunct>
user2 	user2.com 	42.0  		[php] <defunct>
user3 	user3.com 	38.0 	 	[php] <defunct>
user2 	user2.com 	38.0 	 	/usr/bin/php /home/user2/public_html/vbshout.php

There's a dozen or so more in the 15-25% range as well.

Apache/2.2.26
PHP 5.3.28


EDIT: I've heard that dynamic disks in Hyper-V VMs can introduce I/O issues over fixed disks. Does anyone have any experience with this and whether or not it could be leading to the high load? I suspect that the dynamic disk is causing I/O wait or load with mysql which is in turn causing high CPU usage with PHP, but it's just a theory. I plan to convert the system to a fixed disk as soon as I have more scheduled downtime anyway I was just curious if anyone had any experience with this.

 

[thinkbot]

check mysql slow queries and make sure you have php opcode installed, like APC or eaccelerator

 

[cPanelMichael]

Everything was running fine until recently when we installed a chat addon to a client's vBulletin forums. Anytime the chat addon is used the server load skyrockets.

Hello

Have you checked with the developers or support team for this plugin to rule out any issues with the application itself? It's possible there is a flaw in the application that results in high load under heavy usage.

Thank you.