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CPU time (or process time) is the amount of time that a central processing unit (CPU) was used for processing instructions of a computer program or operating system. CPU time is measured in clock ticks or seconds. Sometimes it is useful to convert CPU time into a percentage of the CPU capacity, giving the CPU usage.
The context switch loads the process into the processor and changes the state to "running" while the previously "running" process is stored in a "waiting" state. If a process in the "running" state needs to wait for a resource (wait for user input or file to open, for example), it is assigned the "blocked" state.
t i (processor) is the time process i spends using the CPU, and t i (execution) is the total execution time for the process; i.e. the time for CPU cycles plus I/O cycles to be carried out (executed) until completion of the process. In fact, usually, the sum of all the processor time, used by N processes, rarely exceeds a small fraction of the ...
The SIGALRM, SIGVTALRM and SIGPROF signals are sent to a process when the corresponding time limit is reached. The process sets these time limits by calling alarm or setitimer. The time limit for SIGALRM is based on real or clock time; SIGVTALRM is based on CPU time used by the process; and SIGPROF is based on CPU time used by the process and ...
The final result comes from dividing the number of instructions by the number of CPU clock cycles. The number of instructions per second and floating point operations per second for a processor can be derived by multiplying the number of instructions per cycle with the clock rate (cycles per second given in Hertz) of the processor in question ...
For example, an IBM PC with an Intel 80486 CPU running at 50 MHz will be about twice as fast (internally only) as one with the same CPU and memory running at 25 MHz, while the same will not be true for MIPS R4000 running at the same clock rate as the two are different processors that implement different architectures and microarchitectures ...
The benefit of out-of-order processing grows as the instruction pipeline deepens and the speed difference between main memory (or cache memory) and the processor widens. On modern machines, the processor runs many times faster than the memory, so during the time an in-order processor spends waiting for data to arrive, it could have ...
Process control information is used by the OS to manage the process itself. This includes: Process scheduling state – The state of the process in terms of "ready", "suspended", etc., and other scheduling information as well, such as priority value, the amount of time elapsed since the process gained control of the CPU or since it was suspended.