Comment by ori_b

I can't reproduce. When I run The code is here: https://github.com/gsauthof/osjitter/blob/master/bench_sysca..., here are the numbers on the computers I have:

    AMD Ryzen 7 9700X Desktop:
    ----------------------------------------------------------------------------
    Benchmark                                  Time             CPU   Iterations
    ----------------------------------------------------------------------------
    bench_getuid                            38.6 ns         38.5 ns     18160546
    bench_getpid                            39.9 ns         39.9 ns     17703749
    bench_close                             45.2 ns         45.1 ns     15711379
    bench_syscall                           42.2 ns         42.1 ns     16638675
    bench_sched_yield                       81.7 ns         81.6 ns      8623522
    bench_clock_gettime                     15.9 ns         15.9 ns     44010857
    bench_clock_gettime_tai                 15.9 ns         15.9 ns     43997256
    bench_clock_gettime_monotonic           15.9 ns         15.9 ns     44012908
    bench_clock_gettime_monotonic_raw       15.9 ns         15.9 ns     43982277
    bench_nanosleep0                       49961 ns          370 ns       100000
    bench_nanosleep0_slack1                10839 ns          351 ns      1000000
    bench_nanosleep1_slack1                10878 ns          358 ns      1000000
    bench_pthread_cond_signal               1.37 ns         1.37 ns    503715097
    bench_assign                           0.563 ns        0.562 ns   1000000000
    bench_sqrt                              1.63 ns         1.63 ns    430096636
    bench_sqrtrec                           5.33 ns         5.33 ns    132574542
    bench_nothing                          0.394 ns        0.394 ns   1000000000

    12th Gen Intel(R) Core(TM) i5-12600H
    ----------------------------------------------------------------------------
    Benchmark                                  Time             CPU   Iterations
    ----------------------------------------------------------------------------
    bench_getuid                            70.0 ns         70.0 ns      9985369
    bench_getpid                            71.6 ns         71.6 ns      9763016
    bench_close                             76.7 ns         76.7 ns      9131090
    bench_syscall                           66.8 ns         66.8 ns     10533946
    bench_sched_yield                        160 ns          160 ns      4377987
    bench_clock_gettime                     12.2 ns         12.2 ns     57432496
    bench_clock_gettime_tai                 12.1 ns         12.1 ns     57826299
    bench_clock_gettime_monotonic           12.2 ns         12.2 ns     57736141
    bench_clock_gettime_monotonic_raw       12.3 ns         12.3 ns     57070425
    bench_nanosleep0                       63154 ns        11834 ns        55756
    bench_nanosleep0_slack1                 2933 ns         1700 ns       348675
    bench_nanosleep1_slack1                 2654 ns         1479 ns       467420
    bench_pthread_cond_signal               1.39 ns         1.39 ns    483995101
    bench_assign                           0.868 ns        0.868 ns    821103909
    bench_sqrt                              1.69 ns         1.69 ns    422094139
    bench_sqrtrec                           4.06 ns         4.06 ns    174511095
    bench_nothing                          0.750 ns        0.750 ns    941204159

    AMD Ryzen 5 PRO 7545U Laptop:
    ----------------------------------------------------------------------------
    Benchmark                                  Time             CPU   Iterations
    ----------------------------------------------------------------------------
    bench_getuid                             106 ns          106 ns      6581746
    bench_getpid                             111 ns          111 ns      6271878
    bench_close                              116 ns          116 ns      5944154
    bench_syscall                           85.9 ns         85.9 ns      7317584
    bench_sched_yield                        315 ns          315 ns      2249333
    bench_clock_gettime                     17.6 ns         17.6 ns     39935693
    bench_clock_gettime_tai                 17.6 ns         17.6 ns     39920957
    bench_clock_gettime_monotonic           17.5 ns         17.5 ns     39962966
    bench_clock_gettime_monotonic_raw       17.5 ns         17.5 ns     39561163
    bench_nanosleep0                       52720 ns         3058 ns       100000
    bench_nanosleep0_slack1                13815 ns         2969 ns       244790
    bench_nanosleep1_slack1                13710 ns         2722 ns       254666
    bench_pthread_cond_signal               2.66 ns         2.66 ns    264735233
    bench_assign                           0.930 ns        0.930 ns    813279743
    bench_sqrt                              2.43 ns         2.43 ns    286953468
    bench_sqrtrec                           5.67 ns         5.67 ns    123889652
    bench_nothing                          0.812 ns        0.812 ns    860562208

So, I've tested multiple times in multiple ways, and the results don't seem to match.