Current uClibc-ng version incorrectly calculates clockid in pthread_getcpuclockid (at least for modern kernels). The simplest test program #include <time.h> #include <errno.h> #include <stdio.h> #include <stdlib.h> #include <pthread.h> int main() { clockid_t clk; struct timespec ts; const int err = pthread_getcpuclockid(pthread_self(), &clk); if (err != 0) { errno = err; perror("pthread_getcpuclockid"); return EXIT_FAILURE; } if (clock_gettime(clk, &ts) == -1) { perror("clock_gettime"); return EXIT_FAILURE; } printf("Thread time is %lu.%06lu.\n", ts.tv_sec, ts.tv_nsec / 1000); return EXIT_SUCCESS; } fails with clock_gettime: Invalid argument Tested on Linux 3.4 / MIPS built with GCC 5.4.0. Other implementations, for example musl, use a simple calculation https://git.musl-libc.org/cgit/musl/tree/src/thread/ pthread_getcpuclockid.c Looks strange, but the official glibc repository https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=nptl/ pthread_getcpuclockid.c;hb=HEAD has the same implementation as in uClibc-ng. This fork https://github.com/lattera/glibc/blob/master/ nptl/sysdeps/unix/sysv/linux/pthread_getcpuclockid.c use more accurate approach relying on __NR_clock_getres (defined in the kernel since 2.6.24) with MAKE_THREAD_CPUCLOCK macro copied from the kernel (http://lxr.free-electrons.com/source/include/linux/ posix-timers.h?v=2.6.24#L34, Linux 4.10 has the same one). I propose an intermediate solution: use MAKE_THREAD_CPUCLOCK like computation of clockid when __NR_clock_getres defined and do a fallback to an older implementation when not.