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

Antoine Pitrou solipsis at pitrou.net
Wed Feb 15 18:38:28 CET 2012

On Wed, 15 Feb 2012 18:23:55 +0100 Victor Stinner <victor.stinner at gmail.com> wrote:

Linux supports nanosecond timestamps since Linux 2.6, Windows supports 100 ns resolution since Windows 2000 or maybe before. It doesn't mean that Windows system clock is accurate: in practical, it's hard to get something better than 1 ms :-)

Well, do you think the Linux system clock is nanosecond-accurate?

A nanosecond is what it takes to execute a couple of CPU instructions. Even on a real-time operating system, your nanosecond-precise measurement is already obsolete when it starts being processed by the higher-level application. A single cache miss in the CPU will make the precision worthless.

And in a higher-level language like Python, the execution times of individual instructions are not specified or stable, so the resolution brings you nothing.

"Improved timestamps As computers become faster in general and as Linux becomes used more for mission-critical applications, the granularity of second-based timestamps becomes insufficient. To solve this, ext4 provides timestamps measured in nanoseconds. (...)"

This is a fallacy. Just because ext4 is able to store nanoseconds timestamps doesn't mean the timestamps are accurate up to that point.

Such test is common in build programs like make or scons.

scons is written in Python and its authors have not complained, AFAIK, about timestamp precision.

Regards

Antoine.

More information about the Python-Dev mailing list