Q:

Root cause analysis on a performance issue? 

Can some one give me proper idea on how to perform a Root cause analysis of a performance issue. 
Eg: examine hardware bottle necks,Connectivity issues,SQL server performance,examine the code via white box text ...etc. 

A:

Given you are talking about everything from Hardware to SQL Server to Code, I'm assuming your performance issue is being observed at a high level.   i.e. you have no idea what component(s) may be at fault. 
Here are some ideas of approach when you're not sure where to look:

Recreate and Isolate - By this, I mean try to create the simplest reproduce case that exhibits the issue.   Removing and Adding variables to identify the conditions that create the problem.   Sometimes the reproduce workload will point you in right direction (i.e. only happens under load, or when large data volumes are used, etc.) 
Simple(minimal variables) and repeatable are goals here.  
Monitor - Correlate system health with symptoms being seen.  Introduce tracing where you can to give feedback.   Looking for correlations here.  i.e When things perform bad the cpu is pegged on this server, or when things perform bad we are running a particular process, etc. 
Educated Guess - You or others may have a hunch as to where things are breaking down, hone in on that first.   Protect against assumptions, but have to start somewhere.   
Persist/document - My experience is that when first setting out on tackling a performance issue, early in the process your efforts seem to raise more questions than answers.   You start to question your own sanity.   Document along the way, keep records of what you have tried and what you saw.   Another tip: tell your story to those that will listen, by explaining to others what you have tried in your attempts to find root cause, it can add clarity to yourself when you feel like you're going in circles.  

If you know what area is at fault (DB vs Servers vs Software vs Network.  etc.)  then each one of these have their own technical approaches to narrowing down.   But, I stress again, isolate to simplest recreate.   Having a repeatable recreate in hand, imo, makes the analysis possible. 