VMware released an excellent whitepaper on troubleshooting performance problems in vSphere 4.1. It really is a great resource and start point for anyone who has performance issues in his / her vSphere infrastructure.

The steps discussed in the document use performance data and charts readily available in the vSphere Client and esxtop to aid the troubleshooting flows. Each performance troubleshooting flow has two parts:

1. How to identify the problem using specific performance counters.
2. Possible causes of the problem and solutions to solve it.

Quote for the Introduction of the Performance Troubleshooting for vSphere 4.1 whitepaper :

Performance problems can arise in any computing environment. Complex application behaviors, changing demands, and shared infrastructure can lead to problems arising in previously stable environments. Troubleshooting performance problems requires an understanding of the interactions between the software and hardware components of a computing environment. Moving to a virtualized computing environment adds new software layers and new types of interactions that must be considered when troubleshooting performance problems.

Proper performance troubleshooting requires starting with a broad view of the computing environment and systematically narrowing the scope of the investigation as possible sources of problems are eliminated. Troubleshooting efforts that start with a narrowly conceived idea of the source of a problem often get bogged down in detailed analysis of one component, when the actual source of problem is elsewhere in the infrastructure. In order to quickly isolate the source of performance problems, it is necessary to adhere to a logical troubleshooting methodology that avoids preconceptions about the source of the problems.

The document can be found here. Source is the blog post from the VMware VROOOM! Blog.