PEP 418: Add the accuracy of process and thread time clocks
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Victor Stinner
parent
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commit
f0107e6f66
147
pep-0418.txt
147
pep-0418.txt
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@ -275,21 +275,18 @@ Operating system clocks
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Monotonic clocks
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----------------
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========================= =============== =============== ================ ====================
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Name Resolution Accuracy Adjusted by NTP? Action on suspend
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========================= =============== =============== ================ ====================
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CLOCK_MONOTONIC_RAW 1 ns (*) No Stopped
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gethrtime 1 ns (*) No Not stopped
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CLOCK_HIGHRES 1 ns (*) No ?
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CLOCK_MONOTONIC 1 ns (*) Slewed on Linux Stopped on Linux
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mach_absolute_time() 1 ns (*) No ?
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QueryPerformanceCounter() \- 0.3 ns - 5 ns No Accuracy issue
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GetTickCount[64]() 1 ms 1 ms - 15 ms No Include suspend time
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timeGetTime() 1 ms 1 ms - 15 ms No ?
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========================= =============== =============== ================ ====================
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(*) The accuracy of monotonic clocks depends on the operating system
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and the hardware clock.
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========================= =============== ================ ====================
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Name Resolution Adjusted by NTP? Action on suspend
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========================= =============== ================ ====================
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CLOCK_MONOTONIC_RAW 1 ns No Stopped
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gethrtime 1 ns No Not stopped
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CLOCK_HIGHRES 1 ns No ?
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CLOCK_MONOTONIC 1 ns Slewed on Linux Stopped on Linux
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mach_absolute_time() 1 ns No ?
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QueryPerformanceCounter() \- No Accuracy issue
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GetTickCount[64]() 1 ms No Include suspend time
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timeGetTime() 1 ms No ?
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========================= =============== ================ ====================
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The resolution is the smallest difference between two timestamps
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supported by the format used by the clock. For example,
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@ -306,14 +303,14 @@ Examples of clock accuracy on x86_64:
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========================= ================ ===============
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Name Operating system Accuracy
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========================= ================ ===============
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CLOCK_MONOTONIC_RAW Linux 3.2 1 ns
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CLOCK_MONOTONIC Linux 3.2 1 ns
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CLOCK_HIGHRES SunOS 5.11 2 ns
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CLOCK_MONOTONIC SunOS 5.11 2 ns
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QueryPerformanceCounter Windows Vista 10 ns
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CLOCK_MONOTONIC FreeBSD 8.2 11 ns
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CLOCK_MONOTONIC OpenBSD 5.0 10 ms
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GetTickCount Windows Vista 15.6 ms
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CLOCK_MONOTONIC_RAW Linux 3.2 1 ns
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CLOCK_MONOTONIC Linux 3.2 1 ns
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CLOCK_HIGHRES SunOS 5.11 2 ns
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CLOCK_MONOTONIC SunOS 5.11 2 ns
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QueryPerformanceCounter Windows Seven 10 ns
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CLOCK_MONOTONIC FreeBSD 8.2 11 ns
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CLOCK_MONOTONIC OpenBSD 5.0 10 ms
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GetTickCount Windows Seven 15.6 ms
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========================= ================ ===============
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For CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW, the accuracy of this table is the
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@ -533,18 +530,15 @@ On Solaris, gethrtime() is the same as clock_gettime(CLOCK_MONOTONIC).
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System time clocks
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------------------
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========================= =============== ===============
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Name Resolution Accuracy
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========================= =============== ===============
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CLOCK_REALTIME 1 ns (*)
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GetSystemTimeAsFileTime 100 ns 1 ms - 15 ms
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gettimeofday() 1 µs (*)
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ftime() 1 ms (*)
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time() 1 sec 1 sec
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========================= =============== ===============
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(*) The accuracy of system clocks depends on the operating system and
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the hardware clock.
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========================= ===============
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Name Resolution
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========================= ===============
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CLOCK_REALTIME 1 ns
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GetSystemTimeAsFileTime 100 ns
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gettimeofday() 1 µs
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ftime() 1 ms
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time() 1 sec
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========================= ===============
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Examples of clock accuracy on x86_64:
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@ -555,7 +549,7 @@ CLOCK_REALTIME Linux 3.2 1 ns
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CLOCK_REALTIME FreeBSD 8.2 11 ns
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CLOCK_REALTIME SunOS 5.11 10 ms
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CLOCK_REALTIME OpenBSD 5.0 10 ms
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GetSystemTimeAsFileTime Windows Vista 15.6 ms
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GetSystemTimeAsFileTime Windows Seven 15.6 ms
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========================= ================ ===============
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For CLOCK_REALTIME, the accuracy of this table is the result of clock_getres().
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@ -587,7 +581,7 @@ return the system clock.
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Resolution:
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* clock_gettime(): clock_getres(CLOCK_REALTIME), 1 nanosecond on Linux
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* clock_gettime(): clock_getres(CLOCK_REALTIME)
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* gettimeofday(): 1 microsecond
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* ftime(): 1 millisecond
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* time(): 1 second
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@ -596,14 +590,41 @@ The system time can be set using settimeofday() or
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clock_settime(CLOCK_REALTIME).
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Process and thread time
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-----------------------
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Process time
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------------
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The process and thread time cannot be set. They are not monotonic:
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the clocks stop while the process/thread is idle.
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The process time cannot be set. It is not monotonic: the clocks stop while the
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process is idle.
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Process
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^^^^^^^
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========================= ===============
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Name Resolution
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========================= ===============
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GetProcessTimes() 100 ns
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CLOCK_PROCESS_CPUTIME_ID 1 ns
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clock() \-
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========================= ===============
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Examples of clock accuracy on x86_64:
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========================= ================ ===============
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Name Operating system Accuracy
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========================= ================ ===============
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CLOCK_PROCESS_CPUTIME_ID Linux 3.2 1 ns
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clock() Linux 3.2 1 µs
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clock() SunOS 5.11 1 µs
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clock() FreeBSD 8.2 7.8 ms
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clock() OpenBSD 5.0 10 ms
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GetProcessTimes() Windows Seven 15.6 ms
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========================= ================ ===============
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The accuracy of clock() in this table is the result of 1 / CLOCKS_PER_SEC.
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For CLOCK_PROCESS_CPUTIME_ID, the accuracy of this table is the result of
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clock_getres(). It looks like Linux does not implement clock_getres() and
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always return 1 nanosecond. For GetProcessTimes(), the accuracy is read using
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GetSystemTimeAdjustment().
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Functions
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^^^^^^^^^
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* Windows: GetProcessTimes()
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* clock_gettime(CLOCK_PROCESS_CPUTIME_ID): High-resolution per-process
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@ -622,28 +643,41 @@ Process
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Resolution:
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* clock() rate is CLOCKS_PER_SEC. It was called CLK_TCK in Microsoft
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C before 6.0. On Linux 3, clock() has a resolution of 1
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microsecond.
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C before 6.0.
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* The clock resolution can be read using clock_getres().
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clock_getres(CLOCK_REALTIME) is 1 nanosecond on Linux.
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* GetProcessTimes(): call GetSystemTimeAdjustment().
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Thread time
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-----------
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The thread time cannot be set. It is not monotonic: the clocks stop while the
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thread is idle.
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========================= ===============
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Name Resolution
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========================= ===============
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GetThreadTimes() 100 ns
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CLOCK_THREAD_CPUTIME_ID 1 ns
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========================= ===============
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Examples of clock accuracy on x86_64:
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========================= ================ ===============
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Name Operating system Accuracy
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========================= ================ ===============
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clock() Linux 3.2 1 ms
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clock() SunOS 5.11 1 ms
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clock() FreeBSD 8.2 7.8 ms
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clock() OpenBSD 5.0 10 ms
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CLOCK_THREAD_CPUTIME_ID Linux 3.2 1 ns
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CLOCK_THREAD_CPUTIME_ID FreeBSD 8.2 1 µs
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GetThreadTimes() Windows Seven 15.6 ms
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========================= ================ ===============
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The accuracy of clock() in this table is the result of 1 / CLOCKS_PER_SEC.
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For CLOCK_THREAD_CPUTIME_ID, the accuracy of this table is the result of
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clock_getres(). It looks like Linux does not implement clock_getres() and
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always return 1 nanosecond. For GetThreadTimes(), the accuracy is read using
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GetSystemTimeAdjustment().
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Thread
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^^^^^^
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Functions
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^^^^^^^^^
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* Windows: GetThreadTimes()
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* clock_gettime(CLOCK_THREAD_CPUTIME_ID): Thread-specific CPU-time
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@ -651,15 +685,14 @@ Thread
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Resolution:
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* CLOCK_THREAD_CPUTIME_ID: call clock_getres(). 1 nanosecond on
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Linux.
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* CLOCK_THREAD_CPUTIME_ID: call clock_getres().
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* GetThreadTimes(): call GetSystemTimeAdjustment()
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See also pthread_getcpuclockid().
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Windows: QueryUnbiasedInterruptTime
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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-----------------------------------
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Gets the current unbiased interrupt time from the biased interrupt
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time and the current sleep bias amount. This time is not affected by
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