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time.monotonic() should use a different clock source on Windows #88494
Description
| BPO | 44328 |
|---|---|
| Nosy | @pfmoore, @abalkin, @vstinner, @tjguk, @zware, @eryksun, @zooba, @pganssle, @lunixbochs |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields:
assignee = None
closed_at = None
created_at = <Date 2021-06-06.22:05:07.766>
labels = ['3.11', 'library', 'OS-windows', 'performance']
title = 'time.monotonic() should use a different clock source on Windows'
updated_at = <Date 2021-06-14.21:10:46.833>
user = 'https://github.com/lunixbochs'bugs.python.org fields:
activity = <Date 2021-06-14.21:10:46.833>
actor = 'eryksun'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'Windows']
creation = <Date 2021-06-06.22:05:07.766>
creator = 'lunixbochs2'
dependencies = []
files = []
hgrepos = []
issue_num = 44328
keywords = []
message_count = 12.0
messages = ['395221', '395238', '395490', '395493', '395681', '395683', '395719', '395769', '395771', '395782', '395784', '395849']
nosy_count = 9.0
nosy_names = ['paul.moore', 'belopolsky', 'vstinner', 'tim.golden', 'zach.ware', 'eryksun', 'steve.dower', 'p-ganssle', 'lunixbochs2']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue44328'
versions = ['Python 3.11']
Activity
lunixbochs commentedon Jun 6, 2021
Related to https://bugs.python.org/issue41299#msg395220
Presumably
time.monotonic()on Windows historically used GetTickCount64() because QueryPerformanceCounter() could fail. However, that hasn't been the case since Windows XP: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounterI've run into issues with this when porting python-based applications to Windows. On other platforms, time.monotonic() was a decent precision so I used it. When I ported to Windows, I had to replace all of my time.monotonic() calls with time.perf_counter(). I would pretty much never knowingly call time.monotonic() if I knew ahead of time it could be quantized to 16ms.
My opinion is that the GetTickCount64() monotonic time code in CPython should be removed entirely and only the QueryPerformanceCounter() path should be used.
I also think some of the failure checks could be removed from QueryPerformanceCounter() / QueryPerformanceFrequency(), as they're documented to never fail in modern Windows and CPython has been dropping support for older versions of Windows, but that's less of a firm opinion.
28 remaining items
pythongh-88494: Use QueryPerformanceCounter() for time.monotonic()
pythongh-88494: Use QueryPerformanceCounter() for time.monotonic()
vstinner commentedon Mar 14, 2024
I created #116781 to use QueryPerformanceCounter() for time.monotonic().
vstinner commentedon Mar 14, 2024
See also issue gh-115637.
pythongh-88494: Use QueryPerformanceCounter() for time.monotonic()
gh-88494: Use QueryPerformanceCounter() for time.monotonic() (#116781)
pythongh-88494: Use GetSystemTimePreciseAsFileTime() in time.time()
pythongh-88494: Use GetSystemTimePreciseAsFileTime() in time.time()
vstinner commentedon Mar 15, 2024
time.monotonic() now uses QueryPerformanceCounter() (commit) and has a resolution lower than 1 us. I measured 100 ns (10 MHz) on my Windows 11 VM, whereas before it was 15.6 ms (64 Hz): the updated clock resolution is 156,000x better :-)
Thanks everybody for looking into this issue and providing very useful technical details about these clocks.
Follow-up: see issue gh-63207 to use GetSystemTimePreciseAsFileTime() for time.time().
pythongh-88494: Use QueryPerformanceCounter() for time.monotonic() (p…
pythongh-88494: Use QueryPerformanceCounter() for time.monotonic() (p…
pythongh-88494: Use QueryPerformanceCounter() for time.monotonic() (p…
pythongh-88494: Reduce CLOCK_RES to 1 ms in tests