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[Python-Dev] PEP 410 (Decimal timestamp): the implementation is ready for a review
Mark Shannonmark at hotpy.org
Wed Feb 15 21:15:52 CET 2012
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 loopalmost as frequently as the C program (although not with the overheadof converting to a decimal).Cheers,Mark.
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