Timing profiling using VTune vs. simple Queryperformance counters
Hi , I want to know the difference between timing profiling by using Vtune Analyzer and by using simple Queryperformance counters. is it like this: VTune  is a sampling profiler for x86 systems, both for Linux and Microsoft Windows, A sampling profiler probes the target program's program counter at regular intervals using operating system interrupts. Sampling profiles are typically less accurate and specific, but allow the target program to run at near full speed. means it will not associate time of other processes, running at that time while generating timing profile for any application. while at other end query performance counter will get startime.quadpart and stoptime.quadpart and will calculate total time in executing that process.
With VTune, if you time by Event Based Sampling, at a reasonable sampling rate, you are correct about not impacting the program but getting only approximations on the time spent. When you get past a few hundred samples in the region of interest, the timing is as accurate as any other method. Timers such as QueryPerformance or rdtsc may be superior in those cases where you want to time a designated section of code at the expense of a hundred or so bus clocks. VTune, on the other hand, doesn't require you to know where the hot spots are; it will help you find them, and it offers the ability to select event timers in an effort to find out how the time is spent.