I was trying the nettle-benchmark program and found that it hangs at
startup burning 100% CPU.
Debugging shows this is when measuring benchmark overhead. With a quick
printf of the "ncalls" variable in time_function(), I can see that it
overflows:
time_function ncalls=100 elapsed=0.000010
time_function ncalls=1000 elapsed=0.000003
time_function ncalls=10000 elapsed=0.000002
time_function ncalls=100000 elapsed=0.000002
time_function ncalls=1000000 elapsed=0.000002
time_function ncalls=10000000 elapsed=0.000002
time_function ncalls=100000000 elapsed=0.000002
time_function ncalls=1000000000 elapsed=0.000002
time_function ncalls=1410065408 elapsed=0.000002
time_function ncalls=1215752192 elapsed=0.000002
time_function ncalls=-727379968 elapsed=0.000002
time_function ncalls=1316134912 elapsed=0.000002
time_function ncalls=276447232 elapsed=0.000002
time_function ncalls=-1530494976 elapsed=0.000002
time_function ncalls=1874919424 elapsed=0.000002
time_function ncalls=1569325056 elapsed=0.000002
time_function ncalls=-1486618624 elapsed=0.000002
time_function ncalls=-1981284352 elapsed=0.000002
time_function ncalls=1661992960 elapsed=0.000002
time_function ncalls=-559939584 elapsed=0.000002
time_function ncalls=-1304428544 elapsed=0.000002
time_function ncalls=-159383552 elapsed=0.000002
time_function ncalls=-1593835520 elapsed=0.000002
time_function ncalls=1241513984 elapsed=0.000002
time_function ncalls=-469762048 elapsed=0.000002
time_function ncalls=-402653184 elapsed=0.000002
time_function ncalls=268435456 elapsed=0.000002
time_function ncalls=-1610612736 elapsed=0.000002
time_function ncalls=1073741824 elapsed=0.000002
time_function ncalls=-2147483648 elapsed=0.000002
time_function ncalls=0 elapsed=0.000002
time_function ncalls=0 elapsed=0.000002
time_function ncalls=0 elapsed=0.000002
The elapsed time is the same regardless of ncalls, so I'm thinking that
the compiler as been clever and optimized bench_nothing() into literally
nothing. If I modify it to
static void
bench_nothing(void *arg UNUSED)
{
static int i = 0;
i++;
return;
}
then things work, but of course we're not benchmarking "nothing" anymore.
This is on Fedora 32 with gcc-10.1.1-1.fc32.x86_64
Regards,
Daniel
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