When using the vdso clock_gettime() it looks like that the clock is sometimes not going forward when the process sleeps and the clock also sleeps. This problem only happens with the vdso clock and not with the normal syscall clock. I wrote a small test program which calls the syscall and the vdso version. In the first call they are showing the same time, but after I sleeped for 1 second, they are off by one second. This problem occurs not 100% reliable but I see it pretty often. Only the CLOCK_REALTIME and CLOCK_MONOTONIC seam to be affected CLOCK_REALTIME_COARSE is not affected. I am using an MIPS BE 34Kc V5.6 CPU with two VPEs, but only one is used. This is a Lantiq VRX200 SoC with OpenWrt Linux kernel 4.4 and musl libc. Hauke Here are my measurements: start test syscall: CLOCK_REALTIME: tv_sec: 1454098944, tv_nsec: 463189916 vdso: CLOCK_REALTIME: tv_sec: 1454098944, tv_nsec: 463242196 syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098944, tv_nsec: 456000000 vdso: CLOCK_REALTIME_COARSE: tv_sec: 1454098944, tv_nsec: 456000000 syscall: CLOCK_MONOTONIC: tv_sec: 107, tv_nsec: 28113172 vdso: CLOCK_MONOTONIC: tv_sec: 107, tv_nsec: 32150208 syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 107, tv_nsec: 24678324 vdso: CLOCK_MONOTONIC_COARSE: tv_sec: 107, tv_nsec: 24678324 syscall: CLOCK_MONOTONIC_RAW: tv_sec: 107, tv_nsec: 28263008 vdso: CLOCK_MONOTONIC_RAW: tv_sec: 107, tv_nsec: 28300760 syscall: CLOCK_BOOTTIME: tv_sec: 107, tv_nsec: 28337540 vdso: CLOCK_BOOTTIME: tv_sec: 107, tv_nsec: 28379100 syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3111128 vdso: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3153120 syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3192208 vdso: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3231696 sleep(1) syscall: CLOCK_REALTIME: tv_sec: 1454098945, tv_nsec: 464023036 vdso: CLOCK_REALTIME: tv_sec: 1454098946, tv_nsec: 468077456 syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098945, tv_nsec: 460000000 vdso: CLOCK_REALTIME_COARSE: tv_sec: 1454098945, tv_nsec: 460000000 syscall: CLOCK_MONOTONIC: tv_sec: 108, tv_nsec: 28874940 vdso: CLOCK_MONOTONIC: tv_sec: 109, tv_nsec: 32911852 syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 108, tv_nsec: 24678324 vdso: CLOCK_MONOTONIC_COARSE: tv_sec: 108, tv_nsec: 24678324 syscall: CLOCK_MONOTONIC_RAW: tv_sec: 108, tv_nsec: 29023384 vdso: CLOCK_MONOTONIC_RAW: tv_sec: 108, tv_nsec: 29061372 syscall: CLOCK_BOOTTIME: tv_sec: 108, tv_nsec: 29097912 vdso: CLOCK_BOOTTIME: tv_sec: 108, tv_nsec: 29139864 syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3824540 vdso: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 3865708 syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3904680 vdso: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 3943892 sleep(2) syscall: CLOCK_REALTIME: tv_sec: 1454098947, tv_nsec: 464791376 vdso: CLOCK_REALTIME: tv_sec: 1454098950, tv_nsec: 468847600 syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098947, tv_nsec: 460000000 vdso: CLOCK_REALTIME_COARSE: tv_sec: 1454098947, tv_nsec: 460000000 syscall: CLOCK_MONOTONIC: tv_sec: 110, tv_nsec: 29644468 vdso: CLOCK_MONOTONIC: tv_sec: 113, tv_nsec: 33682152 syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 110, tv_nsec: 24678324 vdso: CLOCK_MONOTONIC_COARSE: tv_sec: 110, tv_nsec: 24678324 syscall: CLOCK_MONOTONIC_RAW: tv_sec: 110, tv_nsec: 29794136 vdso: CLOCK_MONOTONIC_RAW: tv_sec: 110, tv_nsec: 29831728 syscall: CLOCK_BOOTTIME: tv_sec: 110, tv_nsec: 29868576 vdso: CLOCK_BOOTTIME: tv_sec: 110, tv_nsec: 29909920 syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 4547416 vdso: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 4589684 syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 4628872 vdso: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 4668808 sleep(3) syscall: CLOCK_REALTIME: tv_sec: 1454098950, tv_nsec: 465558716 vdso: CLOCK_REALTIME: tv_sec: 1454098956, tv_nsec: 469613960 syscall: CLOCK_REALTIME_COARSE: tv_sec: 1454098950, tv_nsec: 460000000 vdso: CLOCK_REALTIME_COARSE: tv_sec: 1454098950, tv_nsec: 460000000 syscall: CLOCK_MONOTONIC: tv_sec: 113, tv_nsec: 30411308 vdso: CLOCK_MONOTONIC: tv_sec: 119, tv_nsec: 34448236 syscall: CLOCK_MONOTONIC_COARSE: tv_sec: 113, tv_nsec: 24678324 vdso: CLOCK_MONOTONIC_COARSE: tv_sec: 113, tv_nsec: 24678324 syscall: CLOCK_MONOTONIC_RAW: tv_sec: 113, tv_nsec: 30559184 vdso: CLOCK_MONOTONIC_RAW: tv_sec: 113, tv_nsec: 30596676 syscall: CLOCK_BOOTTIME: tv_sec: 113, tv_nsec: 30632568 vdso: CLOCK_BOOTTIME: tv_sec: 113, tv_nsec: 30673204 syscall: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 5262328 vdso: CLOCK_PROCESS_CPUTIME_ID: tv_sec: 0, tv_nsec: 5304576 syscall: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 5343136 vdso: CLOCK_THREAD_CPUTIME_ID: tv_sec: 0, tv_nsec: 5382616
