callgrind#

callgrind - How it Works#

How does it work?

  • valgrind: run-time code instrumentation

  • callgrind is a “tool” using valgrind infrastructure

  • Call-graph analysis, optional cache and branch-prediction analysis

Compared to good old gprof …

  • Sluggishly slow (the price of run-time instrumentation)

  • More accurate

  • Nice graphical tool ⟶ kcachegrind

callgrind - How it is Used#

Compiler and Linker Calls#
$ gcc -c -o program.o program.c
$ gcc -g -c -o program.o program.c # debug info
$ gcc -o program program.o

  • No compiler attention needed

  • Debug information only for source annotation (⟶ kcachegrind)

Producing Output: callgrind.out.<pid>#
$ valgrind --tool=callgrind ./program
...
$ ls callgrind.out.*
callgrind.out.16761

callgrind - Analysis Per Commandline#

Basically records the same information as gprof

  • Flat profile

  • Call Graph

  • All sorts of counters (can detect cache misses etc.)

Most basic analysis tool: callgrind_annotate

$ callgrind_annotate callgrind.out.16761
... unreadable but informative garbage ...

callgrind - Analysis With kcachegrind#

../../../../../../_images/93-03-00-profiling-kcachegrind.jpg

callgrind - Useful Options#

Instrumented code takes very long

  • Start without instrumentation

  • Switch on explicitly during runtime (by PID)

Start Without Instrumentation#
$ valgrind --tool=callgrind --instr-atstart=no ./program
Switch on Instrumentation#
$ callgrind_control --instr=on 16761