cpu-cycles

问题 The Intel manuals for the RDTSC instruction warn that out of order execution can change when RDTSC is actually executed, so they recommend inserting a CPUID instruction in front of it because CPUID will serialize the instruction stream (CPUID is never executed out of order). My question is simple: if they had the ability to make instructions serializing, why didn't they make RDTSC serializing? The entire point of it appears to be to get cycle accurate timings. Is there a situation under which

问题 I have written a program in C. Its a program created as result of a research. I want to compute exact CPU cycles which program consumes. Exact number of cycles. Any idea how can I find that? 回答1: The valgrind tool cachegrind ( valgrind --tool=cachegrind ) will give you a detailed output including the number of instructions executed, cache misses and branch prediction misses. These can be accounted down to individual lines of assembler, so in principle (with knowledge of your exact

问题 I am trying to find a reference for approximately how many CPU cycles various operations require. I don't need exact numbers (as this is going to vary between CPUs) but I'd like something relatively credible that gives ballpark figures that I could cite in discussion with friends. As an example, we all know that floating point division takes more CPU cycles than say doing a bitshift. I'd guess that the difference is that the division is around 100 cycles, where as a shift is 1 but I'm looking

问题 Taken from this SO thread, this piece of code calculates the number of CPU cycles elapsed running code between lines //1 and //2 . $ cat cyc.c #include<stdio.h> static __inline__ unsigned long long rdtsc(void) { unsigned long long int x; __asm__ volatile (".byte 0x0f, 0x31" : "=A" (x)); return x; } int main() { unsigned long long cycles = rdtsc(); //1 cycles = rdtsc() - cycles; //2 printf("Time is %d\n", (unsigned)cycles); return 0; } $ gcc cyc.c -o cyc $ ./cyc Time is 73 $ ./cyc Time is 74 $

问题 In Win32, is there any way to get a unique cpu cycle count or something similar that would be uniform for multiple processes/languages/systems/etc. I'm creating some log files, but have to produce multiple logfiles because we're hosting the .NET runtime, and I'd like to avoid calling from one to the other to log. As such, I was thinking I'd just produce two files, combine them, and then sort them, to get a coherent timeline involving cross-world calls. However, GetTickCount does not increase

问题 I am planning on creating a Sega Master System emulator over the next few months, as a hobby project in Java (I know it isn't the best language for this but I find it very comfortable to work in, and as a frequent user of both Windows and Linux I thought a cross-platform application would be great). My question regards cycle counting; I've looked over the source code for another Z80 emulator, and for other emulators as well, and in particular the execute loop intrigues me - when it is called,

问题 I am planning on creating a Sega Master System emulator over the next few months, as a hobby project in Java (I know it isn't the best language for this but I find it very comfortable to work in, and as a frequent user of both Windows and Linux I thought a cross-platform application would be great). My question regards cycle counting; I've looked over the source code for another Z80 emulator, and for other emulators as well, and in particular the execute loop intrigues me - when it is called,

问题 What is the difference in CPU cycles (or, in essence, in 'speed') between x /= y; and #include <cmath> x = sqrt(y); EDIT: I know the operations aren't equivalent, I'm just arbitrarily proposing x /= y as a benchmark for x = sqrt(y) 回答1: The answer to your question depends on your target platform. Assuming you are using most common x86 cpus, I can give you this link http://instlatx64.atw.hu/ This is a collection of measured instruction latency (How long will it take to CPU to get result after

问题 In a Swing app a method should continue only after user enters a correct answer. The correct answer is stored in a String with user answer being set by a listener to another String . So, the code is while (!correctAnswer.equals(currentAnswer)) { // wait for user to click the button with the correct answer typed into the textfield } // and then continue Is everything fine with this approach or would you somehow refactor it? Doesn't it impose extra penalty on CPU? Here's a somewhat similar

问题 I have a project that dynamically loads in unknown assemblies implementing a specified interface. I don't know the contents or purposes of the assembly, other than it implementing my interface. I need to somehow restrict the amount of processing power available to these assemblies. Processor priority is not what I'm looking for. I can't use a stopwatch and assign a certain amount of time for the assembly to run as the server might be arbitrarily busy. Optimally I'd like to specify some