CLOCK_THREAD_CPUTIME_ID has to look up thread information on each syscall to determine thread specific time elapsed.

CLOCK_MONOTONIC is lower overhead as it is essentially wallclock time.

Currently the opctx spends 1% of cpu time in getThreadCPUTime performing this clock_gettime syscall. This can be optimized by switching to CLOCK_MONOTONIC for a 1% throughput gain or 1% cpu util reduction.