task not relinquishing scheduler busy waiting..

[Chan Kim]

Hi, rtems users,

Please someone help me fix my problem. I think this should be an easy question for those familiar with rtems
I'm implementing a SD card driver and now can read, write files on SD card but it's very slow.
I trigger the request and wait until the processing is done. For completion, thread 3 needs to run getting events from ISR.
Till now, I used rtems_task_wake_after() in thread 1 until it's done which 
is a partial reason why it's so slow.  (unit delay is 1/100 seconds) -- method 1 below.
If I can use a finer grain delay(wait) I could use it. (if there's one please tell me..)

I tried using busy waiting in thread 1(= main thread) -- method 2 below. 
But this busy waiting makes that thread not relinquish the scheduler and runs indefinately.
(thread 3 cannot run, so the processing is not completed. it's deadlock.)
------------  code running in thread 1 --------------
static volatile delaycnt = 0;
static mdelay(int cnt)
{
        int i;
        for(i=0;i<cnt;i++) {
                delaycnt++;
        }
        printk("mdelay exp\n");
}
static void mmc_wait_for_req_done(ald_sd *host, //mmc_host *host,
                struct mmc_request *mrq)
{
        struct mmc_command *cmd;
        int timeout = 0x40000000;
        while (timeout--) {
            if (mrq->completion.done == 1) return;
            //else rtems_task_wake_after(1);    <------ method 1
            else mdelay(1000);                          <-------- method 2
        }
--------------------------

I changed my CONFIGURE_INIT_TASK_PRIORITY to 100. and I created thread 3 using priority 99.
To create task 3 , I used code below,
--------------
    sc = rtems_task_create (rtems_build_name(nm[0], nm[1], nm[2], nm[3]),
        99, //priority
        stacksize,
        RTEMS_PREEMPT|RTEMS_NO_TIMESLICE|RTEMS_NO_ASR|RTEMS_INTERRUPT_LEVEL(0),
        RTEMS_NO_FLOATING_POINT|RTEMS_LOCAL,
        &tid);
...
    sc = rtems_task_start (tid, (rtems_task_entry)entry, (rtems_task_argument)t);
---------------
But I realized rtems_task_start function only makes the thread in 'READY' state, but not actaully executes it.
How do I make task 3 get a chance to run (take scheduler) when task 1 is busy waiting? should I set a scheduler algorithm?
Thanks in advance.

Chan