Im trying to do a little benchmarking of perl, and have patched its distro files to run perl's times() function on each of the ~1900 test files. perl's times() uses man 2 times internally, which I presume reduces to a system-call The standard distro can be run as: HARNESS_TIMER=1 make test but this counts only wall-clock time, and is thus sensitive to system load. times does better, Anyway, the 1st thing I noticed on the times numbers was that they all have 10ms granularity. This agrees with sysconf granularity : $ getconf CLK_TCK 100 but not with linux kernel HZ: $ grep _HZ /boot/config-`uname -r` CONFIG_RCU_FAST_NO_HZ=y CONFIG_NO_HZ=y # CONFIG_HZ_100 is not set # CONFIG_HZ_250 is not set # CONFIG_HZ_300 is not set CONFIG_HZ_1000=y CONFIG_HZ=1000 Confusingly, man 2 times says : NOTES The number of clock ticks per second can be obtained using: sysconf(_SC_CLK_TCK); In POSIX.1-1996 the symbol CLK_TCK (defined in <time.h>) is mentioned as obsolescent. It is obsolete now. but linux (fedora 13) seems to disagree : $ getconf _SC_CLK_TCK getconf: Unrecognized variable `_SC_CLK_TCK' So, the Questions: Why arent they the same ? or what am I missing wrt the relationship between sysconf(CLK_TCK) and kernel HZ ? Is it possible to coax the kernel into counting times in 1ms via some cmd-line option ? I searched Documentation/kernel-parameters.txt, found nothing. is it possible to compile kernel with different HZ options to get the 1ms resolution ? Why doesnt times() also count IO-wait states for a process (and children) ? I note that top reports it (as a system-wide measure) and System Monitor 2.30.0 displays it (same system-wide measure) hypothetically, if IO-wait numbers were collected by times (API/ABI change, so never gonna happen) would it be able to reveal anything ? Id expect it to show measure disk activity due to the process, and arguably be sensitive to system load, unlike user, sys, child-user, child-sys numbers but it still sounds useful. Could process specific IO-wait numbers reveal anything about cache performance ? Do cache misses contribute to IO-wait, or do they get counted in other ways ?