pause
Spin Loop Hint
Improves performance of spin-wait loops (alias for REP NOP).
Pseudocode Operation
// Improves performance of spin-wait loops (alias for REP NOP)Encoding
Operands
Related
More in Base
Reference
Instruction Forms
| Opcode | Instruction | Op/En | 64/32-bit Mode | CPUID | Description |
|---|---|---|---|---|---|
| F3 90 | PAUSE | ZO | Valid Valid | Gives hint to processor that improves performance of spin-wait loops. |
Description
Improves the performance of spin-wait loops. When executing a “spin-wait loop,” processors will suffer a severe performance penalty when exiting the loop because it detects a possible memory order violation. The PAUSE instruction provides a hint to the processor that the code sequence is a spin-wait loop. The processor uses this hint to avoid the memory order violation in most situations, which greatly improves processor performance. For this reason, it is recommended that a PAUSE instruction be placed in all spin-wait loops. An additional function of the PAUSE instruction is to reduce the power consumed by a processor while executing a spin loop. A processor can execute a spin-wait loop extremely quickly, causing the processor to consume a lot of power while it waits for the resource it is spinning on to become available. Inserting a pause instruction in a spinwait loop greatly reduces the processor’s power consumption. This instruction was introduced in the Pentium 4 processors, but is backward compatible with all IA-32 processors. In earlier IA-32 processors, the PAUSE instruction operates like a NOP instruction. The Pentium 4 and Intel Xeon processors implement the PAUSE instruction as a delay. The delay is finite and can be zero for some processors. This instruction does not change the architectural state of the processor (that is, it performs essentially a delaying no-op operation). This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
Operation
Execute_Next_Instruction(DELAY);