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+[[zihintpause]]
+== "Zihintpause" Pause Hint, Version 2.0
+
+The PAUSE instruction is a HINT that indicates the current hart’s rate
+of instruction retirement should be temporarily reduced or paused. The
+duration of its effect must be bounded and may be zero. No architectural
+state is changed.
+(((PAUSE, HINT)))
+(((HINT, PAUSE)))
+
+Software can use the PAUSE instruction to reduce energy consumption
+while executing spin-wait code sequences. Multithreaded cores might
+temporarily relinquish execution resources to other harts when PAUSE is
+executed. It is recommended that a PAUSE instruction generally be
+included in the code sequence for a spin-wait loop.
+(((PAUSE, energy consumption)))
+
+A future extension might add primitives similar to the x86 MONITOR/MWAIT
+instructions, which provide a more efficient mechanism to wait on writes
+to a specific memory location. However, these instructions would not
+supplant PAUSE. PAUSE is more appropriate when polling for non-memory
+events, when polling for multiple events, or when software does not know
+precisely what events it is polling for.
+
+The duration of a PAUSE instruction’s effect may vary significantly
+within and among implementations. In typical implementations this
+duration should be much less than the time to perform a context switch,
+probably more on the rough order of an on-chip cache miss latency or a
+cacheless access to main memory.
+(((PAUSE, duration)))
+
+A series of PAUSE instructions can be used to create a cumulative delay
+loosely proportional to the number of PAUSE instructions. In spin-wait
+loops in portable code, however, only one PAUSE instruction should be
+used before re-evaluating loop conditions, else the hart might stall
+longer than optimal on some implementations, degrading system
+performance.
+
+PAUSE is encoded as a FENCE instruction with _pred_=W, _succ_=0, _fm_=0,
+_rd_=`x0`, and _rs1_=`x0`.
+
+PAUSE is encoded as a hint within the FENCE opcode because some
+implementations are expected to deliberately stall the PAUSE instruction
+until outstanding memory transactions have completed. Because the
+successor set is null, however, PAUSE does not _mandate_ any particular
+memory ordering—hence, it truly is a HINT.
+(((PAUSE, encoding)))
+
+include::images/wavedrom/zihintpause-hint.adoc[]
+[zihintpause-hint]
+.Zihintpause fence instructions
+image::image_placeholder.png[]
+
+Like other FENCE instructions, PAUSE cannot be used within LR/SC
+sequences without voiding the forward-progress guarantee.
+(((PAUSE, LR/RC sequences)))
+
+The choice of a predecessor set of W is arbitrary, since the successor
+set is null. Other HINTs similar to PAUSE might be encoded with other
+predecessor sets.
+