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PEP 418: More QueryPerformanceCounter bugs

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Victor Stinner 2012-03-29 01:57:15 +02:00
parent 9b27cd2bb7
commit 2e4b34df42
1 changed files with 20 additions and 11 deletions
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pep-0418.txt
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@ -237,21 +237,31 @@ Windows: QueryPerformanceCounter
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
High-resolution performance counter. It is monotonic. High-resolution performance counter. It is monotonic.
QueryPerformanceFrequency() gives its frequency. QueryPerformanceFrequency() gives its frequency. Hardward clocks used
by QueryPerformanceCounter:
On Windows XP, QueryPerformanceFrequency() is the processor frequency and * Windows XP: RDTSC instruction of Intel processors, the clock frequency is
QueryPerformanceCounter() is the TSC of the current processor. the frequency of the processor
* Windows 2000: ACPI power management timer, frequency = 3,549,545 Hz
The performance counter value may unexpectedly leap forward because of a * Windows 95/98: 8245 PIT chipset, frequency = 1,193,181 Hz
hardware bug, see the `KB274323`_.
Windows XP had a bug (see `KB896256`_): on a multiprocessor computer,
QueryPerformanceCounter() returned a different value for each processor.
QueryPerformanceFrequency() should only be called once: the frequency will not QueryPerformanceFrequency() should only be called once: the frequency will not
change while the system is running. It fails if the installed hardware does not change while the system is running. It fails if the installed hardware does not
support a high-resolution performance counter. support a high-resolution performance counter.
Bugs:
* The performance counter value may unexpectedly leap forward because of a
hardware bug, see the `KB274323`_.
* On VirtualBox, QueryPerformanceCounter() does not increment the high part
every time the low part overflows, see `Monotonic timers
<http://code-factor.blogspot.fr/2009/11/monotonic-timers.html>`_ (2009).
* VirtualBox had a bug in its HPET virtualized device:
QueryPerformanceCounter() did jump forward by approx. 42 seconds (`issue
#8707 <https://www.virtualbox.org/ticket/8707>`_).
* Windows XP had a bug (see `KB896256`_): on a multiprocessor computer,
QueryPerformanceCounter() returned a different value for each processor.
.. _KB896256: http://support.microsoft.com/?id=896256 .. _KB896256: http://support.microsoft.com/?id=896256
.. _KB274323: http://support.microsoft.com/?id=274323 .. _KB274323: http://support.microsoft.com/?id=274323
@ -434,8 +444,7 @@ static variable, it might be interesting to use this to make sure that the
values returned are indeed monotonic. values returned are indeed monotonic.
* Virtual machines provide less reliable clocks. * Virtual machines provide less reliable clocks.
* QueryPerformanceCounter() has two known bugs: * QueryPerformanceCounter() has known bugs (only one is not fixed yet)
`KB896256`_ (fixed) and `KB274323`_
Python may only workaround a specific known operating system bug: `KB274323`_ Python may only workaround a specific known operating system bug: `KB274323`_
contains a code example to workaround the bug (use GetTickCount() to detect contains a code example to workaround the bug (use GetTickCount() to detect