How to measure elapsed time under Windows?

Grant Edwards invalid at invalid.invalid
Tue Feb 9 23:00:50 CET 2010


On 2010-02-09, Grant Edwards <invalid at invalid.invalid> wrote:
> On 2010-02-09, Jean-Michel Pichavant <jeanmichel at sequans.com> wrote:
>> Grant Edwards wrote:
>>> What's the correct way to measure small periods of elapsed
>>> time.  I've always used time.clock() in the past:
>>>
>>>    start = time.clock()
>>>    [stuff being timed]
>>>    stop  = time.clock()
>>>
>>>    delta = stop-start
>>>
>>>
>>> However on multi-processor machines that doesn't work.
>>> Sometimes I get negative values for delta.  According to
>>> google, this is due to a bug in Windows that causes the value
>>> of time.clock() to be different depending on which core in a
>>> multi-core CPU you happen to be on.   [insert appropriate
>>> MS-bashing here]
>>>
>>> Is there another way to measure small periods of elapsed time
>>> (say in the 1-10ms range)?
>>>
>>> Is there a way to lock the python process to a single core so
>>> that time.clock() works right?
>
>> Did you try with the datetime module ?
>>
>> import datetime
>> t0 = datetime.datetime.now()
>> t1 = t0 - datetime.datetime.now()
>> t1.microseconds
>> Out[4]: 644114
>
> Doesn't work.  datetime.datetime.now has granularity of
> 15-16ms.

time.time() exhibits the same behavior, so I assume that
datetime.datetime.new() ends up making the same libc/system
call as time.time().  From what I can grok of the datetime
module source code, it looks like it's calling gettimeofday().

I can't find any real documentation on the granularity of Win32
gettimeofday() other than a blog post that claims it is 10ms
(which doesn't agree with what my tests show).

-- 
Grant Edwards                   grante             Yow! I feel better about
                                  at               world problems now!
                               visi.com            



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