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Using such calls generally produces the simplest, most efficient, fair, and race-free result. A single call checks, informs the scheduler of the event it is waiting for, inserts a memory barrier where applicable, and may perform a requested I/O operation before returning. Other processes can use the CPU while the caller is blocked.
To reduce inter-CPU bus traffic, code trying to acquire a lock should loop reading without trying to write anything until it reads a changed value. Because of MESI caching protocols, this causes the cache line for the lock to become "Shared"; then there is remarkably no bus traffic while a CPU waits for the lock. This optimization is effective ...
At any specific time, processes can be grouped into two categories: those that are waiting for input or output (called "I/O bound"), and those that are fully utilizing the CPU ("CPU bound"). In primitive systems, the software would often "poll", or "busywait" while waiting for requested input (such as disk, keyboard or network input). During ...
At any specific time, processes can be grouped into two categories: those that are waiting for input or output (called "I/O bound"), and those that are fully utilizing the CPU ("CPU bound"). In early systems, processes would often "poll" or "busy-wait" while waiting for requested input (such as disk, keyboard or network input). During this time ...
The sleep() function call can be repeatedly called for short periods of time to slow the execution of a running program or code. Throttling code in this manner provides a coarse mechanism for mitigating the effects of overheating hardware [7] or easing timing issues for legacy programs. The downside to cycling sleep and running states rather ...
Some second-level CPU caches run slower than the processor core. When the processor needs to access external memory, it starts placing the address of the requested information on the address bus. It then must wait for the answer, that may come back tens if not hundreds of cycles later. Each of the cycles spent waiting is called a wait state.
For example, hardware timers send interrupts to the CPU at regular intervals. Most operating systems execute a HLT instruction when there is no immediate work to be done, putting the processor into an idle state. In Windows NT, for example, this instruction is run in the "System Idle Process". On x86 processors, the opcode of HLT is 0xF4.
However, the idle process does not use up computer resources (even when stated to be running at a high percent). Its CPU time "usage" is a measure of how much CPU time is not being used by other threads. In Windows 2000 and later the threads in the System Idle Process are also used to implement CPU power saving.