System time is the amount of time the CPU was busy executing code in kernel space.User time is the amount of time the CPU was busy executing code in user space.Moreover, depending on what exactly the CPU was doing, the reported values can be subdivided in: Elapsed real time includes I/O time, any multitasking delays, and all other types of waits incurred by the program.ĬPU time or CPU usage can be reported either for each thread, for each process or for the entire system. In contrast, elapsed real time (or simply real time, or wall-clock time) is the time taken from the start of a computer program until the end as measured by an ordinary clock. CPU time allows measurement of the processing power a single program requires, eliminating interference, such as time executed waiting for input or being suspended to allow other programs to run. High CPU usage by a single program may indicate that it is highly demanding of processing power or that it may malfunction for example, it has entered an infinite loop. The CPU usage is used to quantify how the processor is shared between computer programs. In this case the wall time (actual duration elapsed) is irrelevant, the computer may execute the program slower or faster depending on real world variables such as the CPU's temperature, as well as other operating system variables, such as the process's priority. This type of measurement is especially useful when comparing like algorithms that are not trivial in complexity. Without any knowledge of the workings of either algorithm a greater CPU time of bubble sort shows it is less efficient for particular input data than merge sort. However a bubble sort and a merge sort have different running time complexity such that merge sort tends to complete in fewer steps. For example any sorting algorithm takes an unsorted list and returns a sorted list, and will do so in a deterministic number of steps based for a given input list. The CPU time is used to quantify the overall empirical efficiency of two functionally identical algorithms. CPU time and CPU usage have two main uses. Often, it is useful to measure CPU time as a percentage of the CPU's capacity, which is called the CPU usage. The CPU time is measured in clock ticks or seconds. Stime %lu Amount of time that this process has been scheduled in kernel mode.CPU time (or process time) is the amount of time for which a central processing unit (CPU) was used for processing instructions of a computer program or operating system, as opposed to elapsed time, which includes for example, waiting for input/output (I/O) operations or entering low-power (idle) mode. utime %lu Amount of time that this process has been scheduled in user mode. It's determined by summing the utime and stime values that are described in the proc(5) man page. actually using CPU cycles, not sleeping, waiting to run, or waiting for I/O. (alias time).Ĭumulative CPU time is the amount of time the processor spent running the process, i.e. Time the process has been running cputime/realtimeĪnd TIME has two matches, but only one that matches the hh:mm:ss format: cputime TIME cumulative CPU time, "hh:mm:ss" format. For more details, we search for %cpu and find: %cpu %CPU cpu utilization of the process in "#.#" format.Ĭurrently, it is the CPU time used divided by the Integer value of the percent usage over the Press n to find the next match: c C processor utilization. C pcpu cpu utilizationīut that's under the OBSOLETE SORT KEYS header, so is not what we're looking for. If you run man ps then type / Space Shift+C Space Enter, you should see this line.
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