使用 RDTSC 测量时差 - 结果太大

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问题描述

我正在尝试计算运行单个 ASM 指令所需的 CPU 周期数.为了做到这一点，我创建了这个函数:

I'm trying to calculate number of CPU cycles required to run single ASM instruction. In order to do this, I've created this function:

measure_register_op:
    # Calculate time of required for movl operation

    # function setup
    pushl %ebp
    movl %esp, %ebp
    pushl %ebx
    pushl %edi

    xor %edi, %edi

    # first time measurement
    xorl %eax, %eax
    cpuid               # sync of threads
    rdtsc               # result in edx:eax

    # we are measuring instuction below
    movl %eax, %edi

    # second time measurement
    cpuid               # sync of threads
    rdtsc               # result in edx:eax

    # time difference
    sub %eax, %edi

    # move to EAX. Value of EAX is what function returns
    movl %edi, %eax

    # End of function
    popl %edi
    popl %ebx
    mov %ebp, %esp
    popl %ebp

    ret

我在 *.c 文件中使用它:

I'm using it in *.c file:

extern unsigned int measure_register_op();

int main(void)
{

    for (int a = 0; a < 10; a++)
    {
        printf("Instruction took %u cycles \n", measure_register_op());
    }

    return 0;
}

问题是:我看到的值太大了.我现在收到 3684414156.这里会出现什么问题?

The problem is: the values I see are way too large. I'm getting 3684414156 now. What could go wrong here?

从EBX改为EDI，结果还是一样.它必须与 rdtsc 本身有关.在调试器中，我可以看到第二个测量结果为 0x7f61e078 和第一个 0x42999940，减去后仍然给出 1019758392

Changed from EBX to EDI, but result is still similar. It have to be something with rdtsc itself. In debugger I can see that second measurement results with 0x7f61e078 and first 0x42999940, which, after substraction still gives around 1019758392

这是我的makefile.也许我编译不正确:

Here is my makefile. Maybe I'm compiling it incorrectly:

compile: measurement.s measurement.c
    gcc -g measurement.s measurement.c -o ./build/measurement -m32

这是我看到的确切结果:

Here is an exact result I see:

Instruction took 4294966680 cycles
Instruction took 4294966696 cycles
Instruction took 4294966688 cycles
Instruction took 4294966672 cycles
Instruction took 4294966680 cycles
Instruction took 4294966688 cycles
Instruction took 4294966688 cycles
Instruction took 4294966696 cycles
Instruction took 4294966688 cycles
Instruction took 4294966680 cycles

RDTSC

使用 RDTSC 测量时差 - 结果太大

问题描述

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