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Wallclock time is the most natural way to measure performance
Because you want the program to finish sooner rather than later
But measuring wallclock time directly is very tricky
Operating systems like Unix and Windows do pre-emptive multitasking
At any moment the OS might put any process to sleep for a long time
Processes go to sleep when the OS wants to do something else
Sleeping processes consume wallclock time but not CPU time
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Copyright © 2003 M. J. Dominus |