Memtest86 —— Modulo20 算法

一、算法原理

offset = 0 to 19，步长为 20
1.起始地址开始，在每个offset地址写原始 data (以 offset 方式初始化背景数)
2.其余地址写相反之原始 data
3.repeat step2，1次或多次
4.读 offset 地址，比对资料是否正确

二、Memtest86 V5.01 Modulo20 源码

/*
 * Test all of memory using modulo X access pattern.
 */
void modtst(int offset, int iter, ulong p1, ulong p2, int me)
{
	int j, k, l, done;
	ulong *p;
	ulong *pe;
	ulong *start, *end;

	/* Display the current pattern */
        if (mstr_cpu == me) {
		hprint(LINE_PAT, COL_PAT-2, p1);
		cprint(LINE_PAT, COL_PAT+6, "-");
       		dprint(LINE_PAT, COL_PAT+7, offset, 2, 1);
	}

	/* Write every nth location with pattern */
	for (j=0; j<segs; j++) {
		calculate_chunk(&start, &end, me, j, 4);
		end -= MOD_SZ;	/* adjust the ending address */
		pe = (ulong *)start;
		p = start+offset;
		done = 0;
		do {
			do_tick(me);
			BAILR

			/* Check for overflow */
			if (pe + SPINSZ > pe && pe != 0) {
				pe += SPINSZ;
			} else {
				pe = end;
			}
			if (pe >= end) {
				pe = end;
				done++;
			}
			if (p == pe ) {
				break;
			}
/* Original C code replaced with hand tuned assembly code
 *			for (; p <= pe; p += MOD_SZ) {
 *				*p = p1;
 *			}
 */
			asm __volatile__ (
				"jmp L60\n\t" \
				".p2align 4,,7\n\t" \

				"L60:\n\t" \
				"movl %%eax,(%%edi)\n\t" \
				"addl $80,%%edi\n\t" \
				"cmpl %%edx,%%edi\n\t" \
				"jb L60\n\t" \
				: "=D" (p)
				: "D" (p), "d" (pe), "a" (p1)
			);
		} while (!done);
	}

	/* Write the rest of memory "iter" times with the pattern complement */
	for (l=0; l<iter; l++) {
		for (j=0; j<segs; j++) {
			calculate_chunk(&start, &end, me, j, 4);
			pe = (ulong *)start;
			p = start;
			done = 0;
			k = 0;
			do {
				do_tick(me);
				BAILR

				/* Check for overflow */
				if (pe + SPINSZ > pe && pe != 0) {
					pe += SPINSZ;
				} else {
					pe = end;
				}
				if (pe >= end) {
					pe = end;
					done++;
				}
				if (p == pe ) {
					break;
				}
/* Original C code replaced with hand tuned assembly code
 *				for (; p <= pe; p++) {
 *					if (k != offset) {
 *						*p = p2;
 *					}
 *					if (++k > MOD_SZ-1) {
 *						k = 0;
 *					}
 *				}
 */
				asm __volatile__ (
					"jmp L50\n\t" \
					".p2align 4,,7\n\t" \

					"L54:\n\t" \
					"addl $4,%%edi\n\t" \
					"L50:\n\t" \
					"cmpl %%ebx,%%ecx\n\t" \
					"je L52\n\t" \
					  "movl %%eax,(%%edi)\n\t" \
					"L52:\n\t" \
					"incl %%ebx\n\t" \
					"cmpl $19,%%ebx\n\t" \
					"jle L53\n\t" \
					  "xorl %%ebx,%%ebx\n\t" \
					"L53:\n\t" \
					"cmpl %%edx,%%edi\n\t" \
					"jb L54\n\t" \
					: "=b" (k)
					: "D" (p), "d" (pe), "a" (p2),
						"b" (k), "c" (offset)
				);
				p = pe + 1;
			} while (!done);
		}
	}

	/* Now check every nth location */
	for (j=0; j<segs; j++) {
		calculate_chunk(&start, &end, me, j, 4);
		pe = (ulong *)start;
		p = start+offset;
		done = 0;
		end -= MOD_SZ;	/* adjust the ending address */
		do {
			do_tick(me);
			BAILR

			/* Check for overflow */
			if (pe + SPINSZ > pe && pe != 0) {
				pe += SPINSZ;
			} else {
				pe = end;
			}
			if (pe >= end) {
				pe = end;
				done++;
			}
			if (p == pe ) {
				break;
			}
/* Original C code replaced with hand tuned assembly code
 *			for (; p <= pe; p += MOD_SZ) {
 *				if ((bad=*p) != p1) {
 *					error((ulong*)p, p1, bad);
 *				}
 *			}
 */
			asm __volatile__ (
				"jmp L70\n\t" \
				".p2align 4,,7\n\t" \

				"L70:\n\t" \
				"movl (%%edi),%%ecx\n\t" \
				"cmpl %%eax,%%ecx\n\t" \
				"jne L71\n\t" \
				"L72:\n\t" \
				"addl $80,%%edi\n\t" \
				"cmpl %%edx,%%edi\n\t" \
				"jb L70\n\t" \
				"jmp L73\n\t" \

				"L71:\n\t" \
				"pushl %%edx\n\t"
				"pushl %%ecx\n\t"
				"pushl %%eax\n\t"
				"pushl %%edi\n\t"
				"call error\n\t"
				"popl %%edi\n\t"
				"popl %%eax\n\t"
				"popl %%ecx\n\t"
				"popl %%edx\n\t"
				"jmp L72\n"

				"L73:\n\t" \
				: "=D" (p)
				: "D" (p), "d" (pe), "a" (p1)
				: "ecx"
			);
		} while (!done);
	}
}

三、Modulo20 算法简化理解

1. 起始地址开始，在每个offset地址写原始 data (以 offset 方式初始化背景数)

for(j = 0; j < segs; j++) 
{
    p += offset;
    pe -= MOD_SZ;  // MOD_SZ = 20
    for(; p<pe; p+=MOD_SZ) 
    {
        *p = p1;  // p1 为初始化背景数
    }
}

2&3. 其余地址写相反之原始 data，repeat step2

for(i = 0; i < iter; i++)
{
    for(j = 0; j<segs; j++) 
    {
        k = 0;
   
        for(;p<pe;p++) 
        {
             if(k != offset) 
             {
                  *p = p2; // p1 之相反数
             }
    
             if(++k > MOD_SZ-1) 
             {
                   k = 0;
             }
        }
    }
}

4. Compare 数据

for(j = 0; j<segs; j++) 
{ 
     p += offset;
     pe -= MOD_SZ;
  
     for(; p<pe; p+=MOD_SZ) 
     {
          if(*p != p1) 
          {
               error_report();
          }
     } 
}