What is Rdtsc in Linux?

What is Rdtsc in Linux?

rdtsc is a time stamp counter that returns the number of clock ticks from the time the system was last reset. The rdtsc instruction returns the time stamp counter in EDX:EAX.

Is x86_64 32 or 64-bit?

x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging mode.

What is Constant_tsc?

invariant_tsc sysctl on FreeBSD or by the ” constant_tsc ” flag in Linux’s /proc/cpuinfo ). With these processors, the TSC ticks at the processor’s nominal frequency, regardless of the actual CPU clock frequency due to turbo or power saving states.

What is constant TSC?

Constant TSC means that the TSC does not change with CPU frequency changes, however it does change on C state transitions. Invariant. As described in the Intel manual: “The invariant TSC will run at a constant rate in all ACPI P-, C- and T-states” Non-stop.

Is Rdtsc monotonic?

Other than that, yes it’s true that it’s monotonic on one core.

How do you calculate CPU cycles?

1. CPU clock cycles = Instruction count x CPI.
2. CPU execution time =
3. = CPU clock cycles x Clock cycle.
4. = Instruction count x CPI x Clock cycle.
5. T =
6. I.
7. x CPI x C.

How does Rdtsc measure time?

rdtsc timing for a measuring a function

1. Call it in a loop. Aggregate each rdtsc difference within the loop and divide by number of calls. ( Let’s say this is N)
2. Call it in a loop. Get the rdtsc difference of the loop itself and divide by N.

What is TSC scaling?

“TSC scaling” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execu- tion controls (“activate secondary controls”) is 0, VMX non-root operation functions as if all secondary processor-based VM-execution controls (including “TSC scaling”) were 0.

What is invariant TSC?

The invariant TSC means that the TSC continues at a fixed rate regardless of the C-state or frequency of the processor (as long as the processor remains in the ACPI S0 state).

What is Rdtsc instruction?

The rdtsc (Read Time-Stamp Counter) instruction is used to determine how many CPU ticks took place since the processor was reset. Loads the current value of the processor’s time-stamp counter into the EDX:EAX registers. It is commonly used as a timing defense (anti-debugging technique).

What is RDTSC instruction in microprocessor?

The RDTSC is the IA-32/IA-64 (or x86/x64) instruction that loads the current value of the processors’ time stamp into EDX:EAX registers. RDTSC is short for “Read Time-Stamp Counter”. It returns the number of clock cycles since last reset.

How long does RDTSC last on a CPU?

As long as your thread stays on the same CPU core, the RDTSC instruction will keep returning an increasing number until it wraps around. For a 2GHz CPU, this happens after 292 years, so it is not a real issue. You probably won’t see it happen. If you expect to live that long, make sure your computer reboots, say, every 50 years.

What is RDTSC performance timer in C++?

The RDTSC Performance Timer written in C++. The RDTSC is the IA-32/IA-64 (or x86/x64) instruction that loads the current value of the processors’ time stamp into EDX:EAX registers. RDTSC is short for “Read Time-Stamp Counter”. It returns the number of clock cycles since last reset.

Should I use RDTSC to measure time in Linux?

If you do use RDTSC to measure time, you may have surprises when power saving or hyperboost or whatever the multitude of frequency-changing techniques are called kicks in. For actual time, the clock_gettime syscall is surprisingly good under Linux.)