ESM6802是英創(chuàng)公司推出的基于Freescale i.MX6DL雙核處理器(ARM Cortex-A9，主頻1GHz)的高性能工控主板，預(yù)裝正版Windows Embedded Compact 7(WEC7)嵌入式操作系統(tǒng)，WEC7一個最重要的特性就是對多核處理器的支持(Symmetric Multi-Processing(SMP))，下面將通過應(yīng)用程序來測試在單核和多核情況下系統(tǒng)的執(zhí)行情況，為了更直觀的比較，同時參與測試的還有ESM3354，ESM3354是基于TI Coertex-A8處理器的工控主板，CPU主頻1GHz，同樣預(yù)裝WEC7操作系統(tǒng)。

所設(shè)計的測試程序代碼如下，其中的TestSmp函數(shù)有兩個輸入?yún)?shù)，第一參數(shù)表示要創(chuàng)建測試線程的數(shù)量，第二個參數(shù)為所創(chuàng)建線程的運行時長。cbTestSmp是被創(chuàng)建的測試線程，測試線程主要是在一個while循環(huán)中，反復(fù)讀取內(nèi)存變量然后與預(yù)設(shè)值進行比較，在運行設(shè)定的時間后自動退出循環(huán)，其中的threadParam->loops變量會記錄下while循環(huán)總共執(zhí)行的次數(shù)。

typedefstruct_SMP_THREAD_PARAM

{

UINT32 durationMs;

UINT32 threadId;

UINT64 loops;

BOOL bSetAffinity;

UINT32 sandBoxSize;

LPVOID sandBoxStart;

}SMP_THREAD_PARAM, *PSMP_THREAD_PARAM;

ULONGcbTestSmp(LPVOID param)

{

PSMP_THREAD_PARAM threadParam = (PSMP_THREAD_PARAM)param;

DWORD tStart = GetTickCount();

UINT8 *buffer = (UINT8 *)threadParam->sandBoxStart;

wprintf(L"Ahou, Thread %d, running for %d ms\r\n", threadParam->threadId,

threadParam->durationMs);

// Write to sandbox

for(UINT32 i = 0; i < threadParam->sandBoxSize; i++)

{

buffer[i] = (UINT8)(i);

}

while( (GetTickCount() - tStart) < threadParam->durationMs)

{

// Read back from sandbox

for(UINT32 i = 0; i < threadParam->sandBoxSize; i++)

{

if(buffer[i] != (UINT8)(i))

{

wprintf(L"Thread %d : error at byte %d for loop %I64d !!\r\n",

threadParam->threadId, i, threadParam->loops);

}

}

threadParam->loops++;

}

wprintf(L"Thread %d : terminating\r\n", threadParam->threadId);

return0;

}

voidTestSmp(UINT32 nNumOfThread, UINT32 durationMs)

{

UINT32 i;

PSMP_THREAD_PARAM threadParams;

HANDLE *threadHandles;

UINT64 totalLoops = 0;

UINT32 sandBoxSize = 1024 * 128; // 128 kB

HANDLE h_array[1];

threadParams = (PSMP_THREAD_PARAM)malloc(nNumOfThread *sizeof(SMP_THREAD_PARAM));

if(threadParams == NULL)

{

wprintf(L"Failed allocating thread params !\r\n");

return;

}

threadHandles = (HANDLE *)malloc(nNumOfThread *sizeof(HANDLE));

if(threadHandles == NULL)

{

wprintf(L"Failed allocating thread handles !\r\n");

return;

}

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

{

threadParams[i].bSetAffinity = TRUE;

threadParams[i].threadId = i;

threadParams[i].durationMs = durationMs;

threadParams[i].loops = 0;

threadParams[i].sandBoxSize = sandBoxSize;

threadParams[i].sandBoxStart = malloc(sandBoxSize);

threadHandles[i] = CreateThread(NULL, 0, cbTestSmp, &threadParams[i], 0, NULL);

wprintf(L"Thread handle %d : 0x%x\r\n", i, threadHandles[i]);

}

h_array[0] = threadHandles[0];

DWORD res = WaitForSingleObject(h_array[0], INFINITE);

Sleep(500);

if(res == WAIT_TIMEOUT)

{

wprintf(L"Timeout waiting for threads !\r\n");

}

else

{

wprintf(L"All threads exited\r\n");

}

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

{

wprintf(L"Thread %d did run %I64d loops\r\n", i, threadParams[i].loops);

totalLoops += threadParams[i].loops;

free(threadParams[i].sandBoxStart);

CloseHandle(threadHandles[i]);

}

wprintf(L"Total number of loops %I64d (%I64d millions)\r\n", totalLoops,

totalLoops / 1000000);

free(threadHandles);

free(threadParams);

}

將上述測試代碼編譯生成為exe文件，分別在ESM3354和ESM6802上運行，設(shè)置while循環(huán)的執(zhí)行時間均為10000ms，測試結(jié)果如下：

1、創(chuàng)建單個線程

當(dāng)測試程序只創(chuàng)建一個測試線程時，ESM3354的while循環(huán)執(zhí)行了6791次，ESM6802執(zhí)行7493次，雖然ESM6802為雙核處理器，但由于程序只有一個線程，即同一時刻只有一個線程在運行，所以在相同的時間內(nèi)，循環(huán)的次數(shù)僅略多于ESM3354。由于ESM3354和ESM6802的CPU主頻同樣都是1GHz，所以可以認(rèn)為ESM6802多出的循環(huán)次數(shù)也就是Cortex-A8與Cortex-A9在代碼執(zhí)行效率上的差別。

2、創(chuàng)建兩個線程

當(dāng)測試程序創(chuàng)建了兩個線程時，ESM3354會將CPU資源大約平均的分配給兩個線程，如上表中線程1執(zhí)行了3390次，線程2執(zhí)行了3442次，兩個線程總共執(zhí)行的次數(shù)與只創(chuàng)建單個線程測試時的循環(huán)次數(shù)相當(dāng)。ESM6802為雙核CPU，在測試程序有兩個線程的情況下，在同一時刻兩個線程可以同時運行，所以總的循環(huán)次數(shù)大約是單個線程測試時的兩倍。

通過上面的測試可以看到，在多線程情況下，如果操作系統(tǒng)支持多核處理器，那么雙核CPU的運算能力將是單核CPU的兩倍。