What performance impact should one expect when setting UsePerfData=false?

[David Dabbs]

Hello.

What performance impact (improvement) should one expect when setting
UsePerfData=false?


Also, I noticed that PerfDataSaveFile silently overrides PerfDataSaveToFile.

While anyone using this probably knows what they're doing, should
PrintFlagsFinal make this explicit? 


  /* performance data collection */

  product(bool, UsePerfData, true,            
          "Flag to disable jvmstat instrumentation for performance testing"
          "and problem isolation purposes.")  
                                              
  product(bool, PerfDataSaveToFile, false,    
          "Save PerfData memory to hsperfdata_<pid> file on exit")    
                                              
  product(ccstr, PerfDataSaveFile, NULL,      
          "Save PerfData memory to the specified absolute pathname,"  
           "%p in the file name if present will be replaced by pid")  

  // NOTE: If user specifies PerfDataSaveFile, it will save the performance
data
  // to the specified file name no matter whether PerfDataSaveToFile is
specified
  // or not. In other word, -XX:PerfDataSaveFile=.. overrides flag
  // -XX:+PerfDataSaveToFile.

   
  product(intx, PerfDataSamplingInterval, 50 /*ms*/,     
          "Data sampling interval in milliseconds")      
                                              
  product(bool, PerfDisableSharedMem, false,  
          "Store performance data in standard memory")   
                                              
  product(intx, PerfDataMemorySize, 32*K,     
          "Size of performance data memory region. Will be rounded "  
          "up to a multiple of the native os page size.")
                                              
  product(intx, PerfMaxStringConstLength, 1024,          
          "Maximum PerfStringConstant string length before truncation")
                                              
  product(bool, PerfAllowAtExitRegistration, false,      
          "Allow registration of atexit() methods")      
                                              
  product(bool, PerfBypassFileSystemCheck, false,        
          "Bypass Win32 file system criteria checks (Windows Only)")