What does RDTSC do?
What does RDTSC do?
The rdtsc (Read Time-Stamp Counter) instruction is used to determine how many CPU ticks took place since the processor was reset. It is commonly used as a timing defense (anti-debugging technique).
What does RDTSC return?
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.
How do you calculate CPU cycles?
- CPU clock cycles = Instruction count x CPI.
- CPU execution time =
- = CPU clock cycles x Clock cycle.
- = Instruction count x CPI x Clock cycle.
- T =
- I.
- x CPI x C.
What is TSC register?
The Time Stamp Counter (TSC) is a 64-bit register present on all x86 processors since the Pentium. It counts the number of CPU cycles since its reset.
What is TSC Linux?
Protocol. Description. TCP. Transmission Control Protocol: A connection-oriented secure protocol. The data to transmit is first sent by the application as a stream of data then converted by the operating system to the appropriate format.
What is TSC scaling?
This feature, referred to as timestamp-counter scaling (TSC scaling), further extends the capability of virtual-machine monitor (VMM) software that employs the TSC-offsetting mechanism by allowing that software finer control over the value of the timestamp counter (TSC) read during guest virtual machine (VM) execution.
What is CPU cycle time?
CPU cycle Usually, the time required for the execution of one simple processor operation such as an addition; this time is normally the reciprocal of the clock rate.
What is CPU clock cycle?
The clock speed measures the number of cycles your CPU executes per second, measured in GHz (gigahertz). A “cycle” is technically a pulse synchronized by an internal oscillator, but for our purposes, they’re a basic unit that helps understand a CPU’s speed.
What is TSC value?
The Time Stamp Counter (TSC) is a 64-bit register present on all x86 processors since the Pentium. It counts the number of CPU cycles since its reset. The instruction RDTSC returns the TSC in EDX:EAX. In x86-64 mode, RDTSC also clears the upper 32 bits of RAX and RDX.
What is TCP Linux?
What is TSC frequency?
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. Hence TSC ticks are counting the passage of time, not the number of CPU clock cycles elapsed.
What is the RDTSC instruction used for?
Generates the rdtsc instruction, which returns the processor time stamp. The processor time stamp records the number of clock cycles since the last reset. A 64-bit unsigned integer representing a tick count. Header file This routine is available only as an intrinsic.
How to measure the overhead of RDTSC?
Intel and Agner Fog recommend measuring the overhead of RDTSC function and subtracting it from your result. The overhead is relatively low (150-200 clock cycles) and it occurs in all tested functions, so you can neglect it when measuring long functions (e.g., 100 000 clock cycles).
When to use mfence before or after RDTSC?
If software requires RDTSC to be executed only after all previous instructions have executed and all previous loads and stores are globally visible, it can execute the sequence MFENCE;LFENCE immediately before RDTSC.
Why flush the instruction pipeline when serializing RDTSC?
Serializing the instruction stream RDTSC can be executed out-of-order, so you should flush the instruction pipeline to prevent the counter from stopping measurement before the code has actually finished executing.
