A 40-line fix eliminated a 400x performance gap

Re:A 40-line fix eliminated a 400x performance gap by mgaunard on Wednesday January 14, 2026 @09:40AM (#46616560)

clock_gettime is not doing a syscall, it's using vdso.

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Re:A 40-line fix eliminated a 400x performance gap by jerrinot on Wednesday January 14, 2026 @10:07AM (#46616869)

clock_gettime() goes through the vDSO shim, but whether it avoids a syscall depends on the clock ID and (in some cases) the clock source. For thread-specific CPU user time, the vDSO shim cannot resolve the request in user space and must transit into the kernel. In this specific case, there is absolutely a syscall.

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