https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=228669
Bug ID: 228669
Summary: CLOCK_PROCESS_CPUTIME_ID is unnecessarily inaccurate
Product: Base System
Version: CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: cperc...@freebsd.org
clock_gettime(CLOCK_PROCESS_CPUTIME_ID) is far less accurate than
clock_gettime(CLOCK_PROF), even though it seems that they should theoretically
measure the same thing:
CLOCK_PROF
Increments when the CPU is running in user or kernel mode.
CLOCK_PROCESS_CPUTIME_ID
Returns the execution time of the calling process.
It looks like this is due to CLOCK_PROF (aka. calcru) adding time from the
current time slice, while CLOCK_PROCESS_CPUTIME_ID (aka. get_process_cputime
aka rufetch) does not.
Since CLOCK_PROCESS_CPUTIME_ID is the version mandated by POSIX, it would be
nice if it were at least as accurate as the historical BSD profiling clock ID.
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