_mm_sfence对__faststorefence

Question

根据MSDN文档，__faststorefence比_mm_sfence快。在我的时间里，它比我慢三倍多。

平台:Win7 7-64，Visual 2010与x64 SDK。

#include <windows.h>
#include <xmmintrin.h>
#include <intrin.h>

int main(int argc, char* argv[])
{
    int* x = new int;
    __int64 loops = 1000000000; // 1 billion
    __int64 start, elapsed;

    start = __rdtsc();
    for (__int64 i = 0; i < loops; i++)
    {
        *x = 0;
        _mm_sfence();
    }
    elapsed = __rdtsc() - start;

    std::cout << "_mm_sfence: " << elapsed << std::endl
              << "average   : " << double(elapsed) / double(loops) << std::endl;

    start = __rdtsc();
    for(__int64 i = 0; i < loops; i++)
    {
        *x = 0;
        __faststorefence();
    }
    elapsed = __rdtsc() - start;

    std::cout << "__faststorefence: " << elapsed << std::endl
              << average          : " << double(elapsed) / double(loops) << std::end;
}

结果：

• _mm_sfence平均数: 5.7
• __faststorefence平均数: 18.37

__faststorefence生成lock or DWORD PTR [rsp], ebp，ebp已被修改为零，而_mm_sfence生成sfence (不足为奇)

快速仓库栅栏显式地声明它比_mm_sfence更快，所以要么我的测试错了，要么他们错了。有什么想法吗？

Answer 1

我用提供的基准测试过的AMD处理器显示__faststorefence是赢家。

Intel - _mm_sfence: 8.61, __faststorefence: 21.60
AMD 1 - _mm_sfence: 138.21, __faststorefence: 90.96
AMD 2 - _mm_sfence: 55.21, __faststorefence: 20.08

这是在VS 2013。

_mm_sfence =篱笆

__faststorefence =锁或dword ptr，esi

Answer 2

您不能将__fasstorefence (完全栅栏)与_mm_sfence (商店围栏)进行比较。

你需要比较__fasstorefence (全栅栏)和_mm_mfence (m满栅栏).