GNU gprof Profiler Yu Kai Hong Department of Mathematics National Taiwan University July 19, 2008 GNU gprof 1/22

Two types of time profilers Built-in UNIX time profiler - Unix C shell - Others GNU gprof time profiler GNU gprof 2/22

Built-in UNIX time profiler The simplest one. Does not increase extra time cost. Does not provide subroutine relative graph. Does not have to recompile source code. GNU gprof 3/22

Built-in UNIX time profiler Unix C shell u : elapsed user time 0.016s : elapsed system time 0:15.61 : total elapsed time 95.5% : percent of total CPU usage 0+0k : shared/non-shared memory 0+0io : times for performing input/output home]$ time./test u 0.016s 0: % 0+0k 0+0io 0pf+0w GNU gprof 4/22

Built-in UNIX time profiler Others real 0m15.456s : total elapsed time user 0m14.990s : user elapsed time sys 0m0.015s : system elapsed time home]$ time./test real 0m15.456s user 0m14.990s sys 0m0.015s GNU gprof 5/22

GNU gprof time profiler Detail time statistics for each subroutine. Create relative graph for all subroutines. Analysis the program bottleneck. Increase about 30% extra time cost. GNU gprof 6/22

GNU gprof time profiler Recompile the original source code -pg : This option affects both compiling and linking. Add additional commands into source code when compiling code in order to trace all subroutines. Add essential initial settings and statistical processes when linking the objects. gcc –pg SourceCode –o ExecutableFile home]$ gcc –pg test2.c –o test2 GNU gprof 7/22

GNU gprof time profiler Convert produced profile data into text file - ListOfOptions can be omitted. - ExecuteFile can be omitted when the file name is a.out. - StatFiles can be omitted when the file name is gmon.out. gprof ListOfOptions ExecuteFile StatFiles > OutputFile home]$ gprof –b test2 gmon.out > output.txt GNU gprof 8/22

GNU gprof time profiler List of Options -b : omit the table or data illustration on OutputFile. -e(E) SRName : exclude the subroutine SRName from the table (and exclude its elapsed time). -f(F) SRName : only display the subroutine SRName on the table (and its elapsed time). GNU gprof 9/22

GNU gprof time profiler List of Options -s : combine more than one StatFile into single one with default file name gmon.sum. -Z : only display all subroutines table which are unused on the program. GNU gprof 10/22

GNU gprof time profiler Example Program subroutine relative graph GNU gprof 11/22

GNU gprof time profiler Example Program home]$ gcc –pg test.c –o test home]$./test home]$ gprof –b test gmon.out > output home]$ more output GNU gprof 2/22

GNU gprof time profiler Example Program Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls s/call s/call name C B C A B C D GNU gprof 13/22

GNU gprof time profiler Example Program % time : the percent of self seconds from total program elapsed time. cumulative seconds : the seconds cumulate from self seconds. self seconds : total elapsed time called by its parents, not including its children’s elapsed time. equal to (self s/call)*(calls) GNU gprof 14/22

GNU gprof time profiler Example Program calls : total number for each subroutine called by its parents. self s/call : elapsed time for each time called by its parents, not including its children’s elapsed time. total s/call : total elapsed time called by its parents, including its children’s elapsed time. name : subroutine name. GNU gprof 15/22

GNU gprof time profiler Example Program Call graph index %time self children called name [1] main[1] /1 A[2] /1 D[6] /1 main[1] [2] A[2] /1 B1[3] /2 B2[5] GNU gprof 16/22

GNU gprof time profiler Example Program /1 A[2] [3] B1[3] /1 C3[4] /1 C2[7] /1 C1[8] /1 B1[3] [4] C3[4] /2 A[2] /2 D[6] [5] B2[5] GNU gprof 17/22

GNU gprof time profiler Example Program /1 main[1] [6] D[6] /2 B2[5] /1 B1[3] [7] C2[7] /1 B1[3] [8] C1[8] GNU gprof 18/22

Example Program [ ] index value for each subroutine GNU gprof time profiler [2]A [8]C1 [6]D [3]B1 [7]C2 [5]B2 [4]C3 GNU gprof 19/22

Example Program See the second part. A on the left-most means the relation is viewed for A. B1 and B2 are below of A means A is the parent of B1 and B2 (A calls B1 and B2), main is above of A means A is the child of main (A called by main). GNU gprof time profiler name main[1] A[2] D[6] main[1] A[2] B1[3] B2[5] GNU gprof 20/22

Example Program See the second part. 1/2 means subroutine B2 is called by its parents total two times and A calls it only one time. 1 means subroutine A have only one parent. GNU gprof time profiler called name main[1] 1/1 A[2] 1/1 D[6] /1 main[1] 1 A[2] 1/1 B1[3] 1/2 B2[5] GNU gprof 21/22

Example Program See the second part It is viewed for subroutine A. The elapsed time of A’s children is seconds and B1’s children is seconds. Especially, B2’s children is 0 second since B2 doesn’t have any child. GNU gprof time profiler children name main[1] A[2] 4.07 D[6] main[1] A[2] B1[3] 0.00 B2[5] GNU gprof 22/22