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cpu time and wall time in python

VVY answered on August 27, 2023 Popularity 3/10 Helpfulness 7/10

answer cpu time and wall time in python

cpu time and wall time in python

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# In short 
CPU Time: CPU time, also known as process time or user time, 
measures the actual amount of time the CPU spends executing the code

Wall Time: Wall time, also known as real time, measures the total time
elapsed from the start of the code execution to the completion of the code

# In detail
in Python, when you use the %time magic command in IPython or Jupyter Notebook,
it is used to measure the execution time of a single statement or expression. 
It provides information about the CPU time and the wall time, which are two 
different ways to measure time:

CPU Time: CPU time, also known as process time or user time, measures the 
actual amount of time the CPU spends executing the code. It includes the 
time the CPU spends executing your code, as well as any time spent by the 
CPU on behalf of your code, such as system calls or other processes that 
your code invokes. CPU time is usually reported in seconds.

Wall Time: Wall time, also known as real time, measures the total time elapsed 
from the start of the code execution to the completion of the code. It 
includes not only the time your code spends executing but also any time when
your code is waiting for external resources, such as I/O operations 
(e.g., reading from or writing to disk or network operations). 
Wall time is also reported in seconds.

The difference between these two times becomes more apparent when dealing with
code that performs I/O operations, waits for external data, or performs 
multiprocessing. In such cases, the CPU time may be much less than the wall 
time because the code is often waiting for external operations to complete.

Here's a simple example to illustrate the difference:

import time

# Simulate a time-consuming operation (sleep for 2 seconds)
>>> %time time.sleep(2)
CPU times: user 0 ns, sys: 0 ns, total: 0 ns
Wall time: 2.01 s

In this example, the CPU time is close to zero because the CPU was not 
actively processing during the time.sleep(2) call. However, the wall time 
is approximately 2.01 seconds, which includes the time the code was sleeping.

In summary, CPU time measures the actual time the CPU is actively 
executing code, while wall time measures the total time elapsed from 
the start to the end of code execution, including any waiting or I/O operations.

Popularity 3/10 Helpfulness 7/10 Language python

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Tags: cpu-time python wall-time

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Contributed on Aug 27 2023

VVY

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cpu time and wall time in python

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