Understanding time.perf_counter() and time.process_time()

by

There are two distincts types of ‘time’, in this context: absolute time and relative time.

Absolute time is the ‘real-world time’, which is returned by time.time() and which we are all used to deal with. It is usually measured from a fixed point in time in the past (e.g. the UNIX epoch of 00:00:00 UTC on 01/01/1970) at a resolution of at least 1 second. Modern systems usually provide milli- or micro-second resolution. It is maintained by the dedicated hardware on most computers, the RTC (real-time clock) circuit is normally battery powered so the system keeps track of real time between power ups. This ‘real-world time’ is also subject to modifications based on your location (time-zones) and season (daylight savings) or expressed as an offset from UTC (also known as GMT or Zulu time).

Secondly, there is relative time, which is returned by time.perf_counter and time.process_time. This type of time has no defined relationship to real-world time, in the sense that the relationship is system and implementation specific. It can be used only to measure time intervals, i.e. a unit-less value which is proportional to the time elapsed between two instants. This is mainly used to evaluate relative performance (e.g. whether this version of code runs faster than that version of code).

On modern systems, it is measured using a CPU counter which is monotonically increased at a frequency related to CPU’s hardware clock. The counter resolution is highly dependent on the system’s hardware, the value cannot be reliably related to real-world time or even compared between systems in most cases. Furthermore, the counter value is reset every time the CPU is powered up or reset.

time.perf_counter returns the absolute value of the counter. time.process_time is a value which is derived from the CPU counter but updated only when a given process is running on the CPU and can be broken down into ‘user time’, which is the time when the process itself is running on the CPU, and ‘system time’, which is the time when the operating system kernel is running on the CPU on behalf on the process.

More Related Contents:

  1. Python random.choice same output
  2. Python: read object from file in python
  3. Python Variable Declaration
  4. TypeError: ‘
  5. Local (?) variable referenced before assignment [duplicate]
  6. How to deal with certificates using Selenium?
  7. PyQt4 Wait in thread for user input from GUI
  8. If range() is a generator in Python 3.3, why can I not call next() on a range?
  9. Upload Image using POST form data in Python-requests
  10. How to draw a line with matplotlib?
  11. Search for a value in a nested dictionary python
  12. Pickle incompatibility of numpy arrays between Python 2 and 3
  13. Python – Request being blocked by Cloudflare
  14. Regular expression parsing a binary file?
  15. problems with pygame controller support
  16. Python 3 – Can pickle handle byte objects larger than 4GB?
  17. How do order of operations go on Python?
  18. error installing nltk supporting packages : nltk.download()
  19. How can I add python to cmd in windows [closed]
  20. python pandas read_csv delimiter in column data
  21. Extract a subset of key-value pairs from dictionary?
  22. Bare asterisk in function parameters?
  23. create an image with border of certain width in python
  24. Pygame make sprite walk in given rotation
  25. How to reverse a dictionary (whose values are lists) in Python? [duplicate]
  26. Travel directory tree with limited recursion depth
  27. Sound generation / synthesis with python?
  28. Python 3 sqlite parameterized SQL-query
  29. Why do I get “TypeError: not all arguments converted during string formatting” trying to substitute a placeholder like {0} using %?
  30. What are assignment expressions (using the “walrus” or “:=” operator)? Why was this syntax added?

Leave a Comment