I'm experimenting performance counter to find deterministic events.
I originally thought that the number of retired instructions will be the
same for every run of the program with the same input. However, it was not.
The following is the result with the 'task' example provided in libpfm4
package.
./task -e "inst_retired" gcc
gcc: no input files
125240*3* inst_retired
./task -e "inst_retired" gcc
gcc: no input files
125240*5* inst_retired
As you can see above, they are different for each run. I only enabled 'user'
mode counting to exclude any perturbation.
fds[0].hw.exclude_kernel = 1;
fds[0].hw.exclude_idle = 1;
fds[0].hw.exclude_hv = 1;
What is the reason of this unexpected non-determinism?
Best Regards,
Heechul
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