System
RDTSCP
RDTSCP reads the time-stamp counter together with IA32_TSC_AUX, where operating systems keep the number of the processor, after earlier instructions have executed.
- CPUID
- RDTSCP
CPUID.80000001H:EDX[27] - Instructions
- 1 mnemonic
- Processors
- Nehalem, Westmere, Sandy Bridge, Ivy Bridge, Haswell, Broadwell, Skylake, Comet Lake, Cannon Lake, Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Silvermont, Goldmont, Goldmont Plus, Tremont, Snow Ridge, Lakefield, Sierra Forest, Clearwater Forest, Knights Landing, Knights Mill, K10 (Family 10h), Bulldozer, Piledriver, Zen, Zen+, Zen 2
RDTSCP reads the time-stamp counter into EDX:EAX, as RDTSC does, and also the IA32_TSC_AUX MSR into ECX. Operating systems store the processor’s number there (Linux its CPU and NUMA node numbers), so a program learns which processor the time stamp came from.
RDTSCP waits until all earlier instructions have executed and their loads are globally visible, so the code being measured is not cut short; later instructions may still start before it. It is enumerated in CPUID.80000001H:EDX[27]. RDPID reads IA32_TSC_AUX alone.
Instructions
| Mnemonic | Summary | Forms |
|---|---|---|
| RDTSCP | Reads the time-stamp counter into EDX:EAX and IA32_TSC_AUX into ECX, once all earlier instructions have executed. | 1 |
CPUID and processors
XED splits RDTSCP 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.
| ISA set | CPUID | Processors in XED |
|---|---|---|
RDTSCP | RDTSCP | Nehalem, Westmere, Sandy Bridge, Ivy Bridge, Haswell, Broadwell, Skylake, Comet Lake, Cannon Lake, Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Silvermont, Goldmont, Goldmont Plus, Tremont, Snow Ridge, Lakefield, Sierra Forest, Clearwater Forest, Knights Landing, Knights Mill, K10 (Family 10h), Bulldozer, Piledriver, Zen, Zen+, Zen 2 |
Sources
- Intel XED v2026.08.23 (commit
0bcb6237345c): forms, encodings, ISA sets, CPUID bits and chip model. - Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 2 (325383-092, June 2026)
- Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 1 (253665-093, September 2026)
- 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.