内存初始化选用CPU指令疑问

yaos 2008-04-03 03:45:41

做内存清零函数的优化
两个函数
分别用两条指令
一个movdqa，一个movntdq
数据尺寸（双字串长）小时第一个好，数据尺寸大时第二个好
在尺寸为135000-136000范围开始第二个函数表现开始好于一
(纳闷的是不是512k/4=131072)
二级缓存是512k 一级缓存是8k
请问如何切分分界点

#include <stdio.h>

#include <windows.h>



#define TestCount 10000



DWORD TestD[655360];



//应该总假定是双字串

void AsmMemZero0(unsigned long * p, unsigned long t) 

{ 

    __asm 

    { 

    xor eax, eax

	cld

	mov edi, dword ptr [p]

	mov edx, t

	test edx, 0xFFFFFFFF

	je exit0

	test edi, 15  //是否16字节对齐

	je  AsmZero1

    mov ecx, edi

	and ecx, 0xFFFFFFF0

	add ecx, 16

	sub ecx, edi  //得到需要双字复制部分，要和edx比较谁大

    shr ecx, 2 //转换为双字长度

	mov ebx, ecx

	cmp ecx, edx

    ja  AsmZero2  //不足，转尾处理

AsmZero01:

	mov dword ptr [edi], eax

	add edi, 4

	sub ecx, 1

	jne AsmZero01

    sub edx, ebx

	je exit0  //是否刚好

AsmZero1: //16字节对齐

	mov ecx, edx

	shr ecx, 2

	je AsmZero2  //是否不足16字节

    pxor xmm0, xmm0

AsmZero11:

	movdqa [edi], xmm0

	add edi, 16

	sub ecx, 1

	jne AsmZero11

AsmZero2:

	mov ecx, edx

	and ecx, 15

	je exit0

AsmZero3:

	mov dword ptr [edi], eax

	add edi, 4

	sub ecx, 1

	jne AsmZero3

exit0:

	} 

} 



//应该总假定是双字串

void AsmMemZero1(unsigned long * p, unsigned long t) 

{ 

    __asm 

    { 

    xor eax, eax

	cld

	mov edi, dword ptr [p]

	mov edx, t

	test edx, 0xFFFFFFFF

	je exit0

	test edi, 15  //是否16字节对齐

	je  AsmZero1

    mov ecx, edi

	and ecx, 0xFFFFFFF0

	add ecx, 16

	sub ecx, edi  //得到需要双字复制部分，要和edx比较谁大

    shr ecx, 2 //转换为双字长度

	mov ebx, ecx

	cmp ecx, edx

    ja  AsmZero2  //不足，转尾处理

AsmZero01:

	mov dword ptr [edi], eax

	add edi, 4

	sub ecx, 1

	jne AsmZero01

    sub edx, ebx

	je exit0  //是否刚好

AsmZero1: //16字节对齐

	mov ecx, edx

    pxor xmm0, xmm0

	shr ecx, 2

	je AsmZero2  //是否不足16字节

AsmZero11:

	movntdq [edi], xmm0

	add edi, 16

	sub ecx, 1

	jne AsmZero11

AsmZero2:

	mov ecx, edx

	and ecx, 15

	je exit0

AsmZero3:

	mov dword ptr [edi], eax

	add edi, 4

	sub ecx, 1

	jne AsmZero3

exit0:

	sfence

	} 

} 



//应该总假定是双字串

void AsmMemZeroALU(unsigned long * p, unsigned long t) 

{ 

    __asm 

    { 

    xor eax, eax

	cld

	mov edi, dword ptr [p]

	mov ecx, t

	test ecx, 0xFFFFFFFF

	je exit0

	rep stosd

exit0:

	} 

}



int main(void)

{

	UINT64 s_u64Frequency = 1;

    UINT64 s_u64Start, s_u64End;

	unsigned long i, TestSize;



	printf("Input Test Size: ");

	scanf("%ld", &TestSize);

	SetThreadPriority(GetCurrentThread(),   THREAD_PRIORITY_TIME_CRITICAL); 



	QueryPerformanceFrequency((LARGE_INTEGER *)&s_u64Frequency );

	QueryPerformanceCounter((LARGE_INTEGER *)&s_u64Start );

	for (i = 0; i < TestCount; i ++)

		AsmMemZero0(&TestD[0], TestSize);

	QueryPerformanceCounter((LARGE_INTEGER *)&s_u64End );



	printf( "func 0 Elapsed time: %.3f ms\n",

		(double)(( s_u64End - s_u64Start ) * 1000.0 / (double)s_u64Frequency ));



	QueryPerformanceFrequency((LARGE_INTEGER *)&s_u64Frequency );

	QueryPerformanceCounter((LARGE_INTEGER *)&s_u64Start );

	for (i = 0; i < TestCount; i ++)

		AsmMemZero1(&TestD[0], TestSize);

	QueryPerformanceCounter((LARGE_INTEGER *)&s_u64End );



	printf( "func 1 Elapsed time: %.3f ms\n",

		(double)(( s_u64End - s_u64Start ) * 1000.0 / (double)s_u64Frequency ));



	return 0;

}