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Improving the support for ARM in IgProf

Improving the support for ARM in IgProf. Filip Nybäck CERN/GSoC video meeting 28 August, 2014. IgProf. profiler program measuring mainly performance and memory usage of other programs at run-time find performance bottlenecks parts of the code worth optimising. What has been done?.

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Improving the support for ARM in IgProf

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  1. Improving the support for ARM in IgProf • Filip Nybäck • CERN/GSoC video meeting 28 August, 2014

  2. IgProf • profiler • program measuring mainly performance and memory usage of other programs at run-time • find performance bottlenecks • parts of the code worth optimising

  3. What has been done? • IgProf ported to 64-bit ARM • fast stack trace in libunwind ported to • 64-bit ARM • 32-bit ARM • bonus: simple energy profiling module

  4. Function instrumentation • the profiler gets between the function call and the function itself • collect function parameters and the return value • collect the number of calls application IgProf C library ... malloc(...) ... malloc hook for malloc

  5. Function instrumentation generate jumps Text • identify and patch • PC-relative instructions • load instructions • address calculation instructions • relative jump instructions

  6. Stack tracing • An example: • function a calls function b,function b calls function c • the stack trace: [c, b, a] • Stack tracing in libunwind: • uses unwind information • calculates the state of the registers in the previous frame • for stack tracing only the PC register is interesting The stack: a b c the stack grows downward

  7. Fast stack tracing in libunwind • only a subset of the state in each frame is needed to calculate the PC • cache the information about how to calculate the subset of the state • port to ARM • differences in the architectures and calling conventions • where the return address is stored (on the stack, in a register, both) • which register is used to find the previous frame (stack pointer, frame pointer, some other register)

  8. Results • stack tracing only • time(standard stack trace) = 20…30 * time(fast stack trace) • memory profiling with IgProf • time(IgProf + standard stack trace) = 7…8 * time(IgProf + fast stack trace)

  9. Energy profiling module • gets energy measurements from the RAPL (Running Average Power Limit) interface on recent Intel processors • through the PAPI library • based on sampling • highly experimental

  10. Principle of operation • The amount of energy consumed since the previous sampling event is attributed to the current location of execution amount of energy t n n–1 n–2 sampling interval

  11. Example energy profile

  12. Thank you! • questions • comments

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