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System

RDPID

RDPID reads IA32_TSC_AUX, where operating systems keep the number of the processor, without the time stamp that RDTSCP also returns.

CPUID
RDPID
CPUID.(EAX=07H,ECX=0):ECX[22]
Instructions
1 mnemonic
Processors
Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Goldmont Plus, Tremont, Snow Ridge, Lakefield, Sierra Forest, Clearwater Forest, Zen 2

RDPID reads the IA32_TSC_AUX MSR into a register, without the time stamp that RDTSCP also returns and without its wait for earlier instructions. Operating systems keep the processor’s number in that MSR; Linux stores the CPU number in the low 12 bits and the NUMA node above them, and its vDSO reads them with RDPID for getcpu() where the processor has it. The operand is 64 bits in 64-bit mode and 32 bits otherwise.

Instructions

Mnemonics with at least one form in RDPID. Each page lists all forms of the mnemonic, including those of other extensions.
MnemonicSummaryForms
RDPIDReads the processor ID that the kernel stored in IA32_TSC_AUX (on Linux, the CPU and node number) without reading the time-stamp counter.2

CPUID and processors

XED splits RDPID 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 RDPID. Alternatives are separated by “or”; processors follow XED’s chip model, which covers AMD processors up to Zen 2.
ISA setCPUIDProcessors in XED
RDPID

RDPID
CPUID.(EAX=07H,ECX=0):ECX[22] RDPID

Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Goldmont Plus, Tremont, Snow Ridge, Lakefield, Sierra Forest, Clearwater Forest, Zen 2

Sources

  1. Intel XED v2026.08.23 (commit 0bcb6237345c): forms, encodings, ISA sets, CPUID bits and chip model.
  2. Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 2 (325383-092, June 2026)
  3. Linux arch/x86/include/asm/segment.h: the CPU and node number in IA32_TSC_AUX

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.