较小的管道如何加速数据流?

if (0 == CreatePipe(&hRead,&hWrite,0,1024*1024))
{
printf("CreatePipe failed\n");
return success;
}

while ((bytesReq = (FileSize - offset)) != 0)
{


//Send data to Decoder.cpp thread, converting to human readable CSV
        if ( (0 == WriteFile(hWrite,
                               readBuff,
                               bytesReq,
                               &bytesWritten,
                               0) ) || 
                               (bytesWritten != bytesReq) )
        {
             printf("WriteFile failed error = %d\n",GetLastError());
             break;
        } 

}  

Only 4 bytes at a time being read in at another thread, on other end of pipe.  

当我把管道变小的时候,发送和阅读的总时间就变小了。

将管道尺寸更改为
1024*1024=2分钟(原尺寸)

10000=1分33秒

怎么会这样?