title: Performance Counter Information required
body: <p>I need to learn how performance counter works for my research project.
  I have understood how hardware supports the monitoring of events.Intel manual gives description on how the performance monitoring units on the chip helps to get the counters.
  I also have learned how the MSR module gets the information of the msr registers for various events.</p>
  
  <p>I need to learn the following things.</p>
  
  <p>1) How performance monitoring tools are used for multiple processes simultaneously. 
  I think all the registers will be saved during context switch and are loaded when the process start again.Browsing Internet I got something like "pfm_context_load" and "pfm_context_unload" but it didn't had much info......-> <strong>" I need more detailed information on how it works,so please provide some links,documentation which can help me achieve my understanding"</strong></p>
  
  <p>2) Also how performance counters work in virtual environment? And what are the problems measuring  the counters in such environment? I have browsed through few papers and have some info, But need more detail information.</p>
  
  <p>So if anyone can guide me with some documentation on these topics or at least guide me on where should I search for all these info with be a great help! ...</p>
  
  <p>If this is not the right forum then please direct me towards right place..</p>
  
  <p>Thanks</p>
  
  <p>Anup</p>