Intel® 64 and IA-32 Architectures Optimization Reference Manual

APPLICATION PERFORMANCE TOOLSA.2.1.1Time-based SamplingTime-based sampling (TBS) uses an operating system’s (OS) timer to periodicallyinterrupt the processor to collect samples. The sampling interval is user definable.TBS is useful for identifying the software on your computer that is taking the mostCPU time. This feature is only available in the Windows version of the VTune AnalyzerA.2.1.2Event-based SamplingEvent-based sampling (EBS) can be used to provide detailed information on thebehavior of the microprocessor as it executes software. Some of the events that canbe used to trigger sampling include clockticks, cache misses, and branch mispredictions.The VTune analyzer indicates where micro architectural events, specific to theIntel Core microarchitecture, Pentium 4, Pentium M and Intel Xeon processors, occurthe most often. On processors based on Intel Core microarchitecture, it is possible tocollect up to 5 events (three events using fixed-function counters, two events usinggeneral-purpose counters) at a time from a list of over 400 events (see Appendix A,“Performance Monitoring Events” of Intel® 64 and IA-32 Architectures SoftwareDeveloper’s Manual, Volume 3B). On Pentium M processors, the VTune analyzer cancollect two different events at a time. The number of the events that the VTuneanalyzer can collect at once on the Pentium 4 and Intel Xeon processor depends onthe events selected.Event-based samples are collected periodically after a specific number of processorevents have occurred while the program is running. The program is interrupted,allowing the interrupt handling driver to collect the Instruction Pointer (IP), loadmodule, thread and process ID's. The instruction pointer is then used to derive thefunction and source line number from the debug information created at compile time.The Data can be displayed as horizontal bar charts or in more detail as spread sheetsthat can be exported for further manipulation and easy dissemination.A.2.1.3Workload CharacterizationUsing event-based sampling and processor-specific events can provide usefulinsights into the nature of the interaction between a workload and the microarchitecture.A few metrics useful for workload characterization are discussed in Appendix B.The event lists available on various Intel processors can be found in Appendix A,“Performance Monitoring Events” of Intel® 64 and IA-32 Architectures SoftwareDeveloper’s Manual, Volume 3B.A.2.2Call GraphCall graph helps you understand the relationships between the functions in yourapplication by providing timing and caller/callee (functions called) information. Callgraph works by instrumenting the functions in your application. Instrumentation isthe process of modifying a function so that performance data can be captured whenthe function is executed. Instrumentation does not change the functionality of theA-11