Hi, list How to comfirm whether __GI___clock_gettime() implemented as fast system call or not on x86_64 platform with Linux 4.19.84? Here is some related backtrace log(hope there is some hint on this question): (gdb) bt #0 0x00007ffc41da89fa in ?? () #1 0x00007fa90785aaf0 in ?? () #2 0x00007fa905a16876 in __GI___clock_gettime (clock_id=0, tp=0x7fa90785aac0) at ../sysdeps/unix/clock_gettime.c:115 Thank you for your attention to this matter.