rdtsc

来源： https://stackoverflow.com/questions/25696039/intercept-rdtsc-instruction-from-guest-vm-userspace-in-kvm

来源： https://stackoverflow.com/questions/25696039/intercept-rdtsc-instruction-from-guest-vm-userspace-in-kvm

问题 I used to benchmark Linux System Calls with rdtsc to get the counter difference before and after the system call. I interpreted the result as wall clock timer since TSC increments at constant rate and does not stop when entering halt state. The Invariant TSC concept is described as The invariant TSC will run at a constant rate in all ACPI P-, C-. and T-states. Can a constant non-invariant tsc change frequency when changing state from C0 (operating) to C1 (halted)? My current view is that it

问题 I used to benchmark Linux System Calls with rdtsc to get the counter difference before and after the system call. I interpreted the result as wall clock timer since TSC increments at constant rate and does not stop when entering halt state. The Invariant TSC concept is described as The invariant TSC will run at a constant rate in all ACPI P-, C-. and T-states. Can a constant non-invariant tsc change frequency when changing state from C0 (operating) to C1 (halted)? My current view is that it

问题 Currently I am trying to measure number of clock cycles taken to complete an operation by two different programming languages on same environment. (without using an OS) Currently I am using Qemu-i386 emulator and using rdtsc to measure the clock cycles. /* Return the number of CPU ticks since boot. */ static inline u64 rdtsc(void) { u32 hi, lo; // asm("cpuid"); asm("rdtsc" : "=a" (lo), "=d" (hi)); return ((u64) lo) | (((u64) hi) << 32); } Taking the difference between rdtsc before and after

问题 Currently I am trying to measure number of clock cycles taken to complete an operation by two different programming languages on same environment. (without using an OS) Currently I am using Qemu-i386 emulator and using rdtsc to measure the clock cycles. /* Return the number of CPU ticks since boot. */ static inline u64 rdtsc(void) { u32 hi, lo; // asm("cpuid"); asm("rdtsc" : "=a" (lo), "=d" (hi)); return ((u64) lo) | (((u64) hi) << 32); } Taking the difference between rdtsc before and after

问题 For many years x86 CPUs supported the rdtsc instruction, which reads the "time stamp counter" of the current CPU. The exact definition of this counter has changed over time, but on recent CPUs it is a counter that increments at a fixed frequency with respect to wall clock time, so it is very useful as building block for a fast, accurate clock or measuring the time taken by small segments of code. One important fact about the rdtsc instruction isn't ordered in any special way with the

问题 For many years x86 CPUs supported the rdtsc instruction, which reads the "time stamp counter" of the current CPU. The exact definition of this counter has changed over time, but on recent CPUs it is a counter that increments at a fixed frequency with respect to wall clock time, so it is very useful as building block for a fast, accurate clock or measuring the time taken by small segments of code. One important fact about the rdtsc instruction isn't ordered in any special way with the

问题 As far as I know, the main difference in runtime ordering in a processor with respect to rdtsc and rdtscp instruction is that whether the execution waits until all previous instructions are executed locally. In other words, it means lfence + rdtsc = rdtscp because lfence preceding the rdtsc instruction makes the following rdtsc to be executed after all previous instruction finish locally. However, I've seen some example code that uses rdtsc at the start of measurement and rdtscp at the end.

问题 I am running this test on a cpu with constant_tsc and nonstop_tsc $ grep -m 1 ^flags /proc/cpuinfo | sed 's/ /\n/g' | egrep "constant_tsc|nonstop_tsc" constant_tsc nonstop_tsc Step 1: Calculate the tick rate of the tsc: I calculate _ticks_per_ns as the median over a number of observations. I use rdtscp to ensure in-order execution. static const int trials = 13; std::array<double, trials> rates; for (int i = 0; i < trials; ++i) { timespec beg_ts, end_ts; uint64_t beg_tsc, end_tsc; clock