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System

MONITORX and MWAITX (AMD)

MONITORX and MWAITX are AMD's MONITOR and MWAIT for every privilege level, with a timeout on the wait.

An AMD extension: Intel processors do not have this instruction.

CPUID
MONITORX
CPUID.80000001H:ECX[29]
Instructions
2 mnemonics
Processors
Zen 2, Zen 3, Zen 4, Zen 5, Zen 6
Linux flag
mwaitx

Instructions

Mnemonics with at least one form in MONITORX. Each page lists all forms of the mnemonic, including those of other extensions.
MnemonicSummaryForms
MONITORXSets up the address range that MWAITX waits on, like MONITOR but usable at any privilege level.1
MWAITXWaits until a store hits the range that MONITORX set up, or a timeout in EBX expires, at any privilege level.1

CPUID and processors

XED splits MONITORX into 1 ISA set. Software can use a form when the processor reports every CPUID bit of one alternative of the form's ISA set.

XED ISA sets of MONITORX. Alternatives are separated by “or”; processors follow XED’s chip model, whose AMD processors end with Zen 2, and the CPU data of this site for Zen 3 to Zen 6.
ISA setCPUIDProcessors
MONITORX

MONITORX
CPUID.80000001H:ECX[29] MONITORX

Zen 2, Zen 3, Zen 4, Zen 5, Zen 6

Note: XED gives MONITORX and MWAITX to its Zen 2 chip alone; GCC's -march=bdver4 (Excavator) and -march=znver1 and later enable them.

Sources

  1. Intel XED v2026.08.23 (commit 0bcb6237345c): forms, encodings, ISA sets, CPUID bits and chip model.
  2. The CPU data of x86-64.net: Zen 3 to Zen 6, from GCC’s -march feature sets and AMD’s Processor Programming References, which the page of each processor cites.
  3. AMD64 Architecture Programmer's Manual, Volume 3: General-Purpose and System Instructions (24594, rev. 3.36, March 2024), Wayback Machine copy of AMD's PDF

The tables are derived from Intel XED, Copyright Intel Corporation, licensed under the Apache License 2.0; x86-64.net converted and reformatted them. The text is our own.