[Python-Dev] PEP 410 (Decimal timestamp): the implementation is ready for a review

[Mark Shannon]

Antoine Pitrou wrote:
> On Wed, 15 Feb 2012 20:56:26 +0100
> "Martin v. Löwis" <martin at v.loewis.de> wrote:
>> With the quartz in Victor's machine, a single clock takes 0.3ns, so
>> three of them make a nanosecond. As the quartz may not be entirely
>> accurate (and also as the CPU frequency may change) you have to measure
>> the clock rate against an external time source, but Linux has
>> implemented algorithms for that. On my system, dmesg shows
>>
>> [    2.236894] Refined TSC clocksource calibration: 2793.000 MHz.
>> [    2.236900] Switching to clocksource tsc
> 
> But that's still not meaningful. By the time clock_gettime() returns,
> an unpredictable number of nanoseconds have elapsed, and even more when
> returning to the Python evaluation loop.
> 
> So the nanosecond precision is just an illusion, and a float should
> really be enough to represent durations for any task where Python is
> suitable as a language.

I reckon PyPy might be able to call clock_gettime() in a tight loop
almost as frequently as the C program (although not with the overhead
of converting to a decimal).

Cheers,
Mark.