x86-64.net

Memory, caches and atomics

MCOMMIT

MCOMMIT waits until earlier stores to memory with delayed error reporting have completed and says in CF whether any of them failed.

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

CPUID
MCOMMIT
CPUID.80000008H:EBX[8]
Instructions
1 mnemonic
Processors
Zen 2, Zen 3

Note: Only the EPYC 7002 (Zen 2) and EPYC 7003 (Zen 3) server processors have MCOMMIT. AMD's references for the Ryzen processors of Zen 2 and Zen 3 leave CPUID_Fn80000008_EBX[MCOMMIT] (bit 8) clear, and so do its references for Zen 4 and Zen 5, EPYC included.

Instructions

Mnemonics with at least one form in MCOMMIT. Each page lists all forms of the mnemonic, including those of other extensions.
MnemonicSummaryForms
MCOMMITWaits until earlier stores to memory with delayed error reporting have completed, and clears CF if any of them failed.1

CPUID and processors

XED splits MCOMMIT 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 MCOMMIT. 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
MCOMMIT

MCOMMIT
CPUID.80000008H:EBX[8] MCOMMIT

Zen 2, Zen 3

Note: Only the EPYC 7002 (Zen 2) and EPYC 7003 (Zen 3) server processors have MCOMMIT. AMD's references for the Ryzen processors of Zen 2 and Zen 3 leave CPUID_Fn80000008_EBX[MCOMMIT] (bit 8) clear, and so do its references for Zen 4 and Zen 5, EPYC included.

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. 3.38, July 2026)

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.