clflush or any openCL API is taking more time once kernel execution is completed.

Altera_Forum · ‎06-12-2018

In function1(), we are launching kernel, but we are not waiting for kernel completion. After kernel launch, some processing is happening on CPU which takes around 300msec. While processing on CPU we have triggered for the kernel execution status along with timer. It is showing status as running for few iterations and time taken by clFlush is negligible. Once kernel execution is completed clFlush is consuming 6711 micro sec(Instead of clfinish, if we have clenqueuereadbuffer it is also consuming the same time). Why is it consuming more time once the execution is completed? Is there any alternate method to reduce the time?

void function1()

{

printf("In function-1\n");

...

err = clEnqueueTask(commandQueue[0], kernel, 0, NULL, &kernel_event[0]);

if (CL_SUCCESS != err) {

printf("Error in clEnqueueTask kernel-1 %d\n\n", err);

exit(-1);

}

void function2()

{

printf("In function-2\n");

struct timeval start_timer, end_timer;

gettimeofday(&start_timer, NULL);

err = clEnqueueReadBuffer(commandQueue[0], dstOut1, CL_TRUE, 0, 120 * 23 * sizeof(cl_short2), output1, 0, NULL, NULL);

if (CL_SUCCESS != err) {

printf("Error in clEnqueueReadBuffer dstOut1 %d\n", err);

exit(-1);

}

gettimeofday(&end_timer, NULL);

time_taken = ((end_timer.tv_sec * 1000000 + end_timer.tv_usec) - (start_timer.tv_sec * 1000000 + start_timer.tv_usec));

printf("Time taken by clEnqueueReadBuffer-1 %ld\n", time_taken);

gettimeofday(&start_timer, NULL);

err = clEnqueueReadBuffer(commandQueue[0], dstOut2, CL_TRUE, 0, 120 * 23 * sizeof(cl_short2), output2, 0, NULL, NULL);

if (CL_SUCCESS != err) {

printf("Error in clEnqueueReadBuffer dstOut2 %d\n", err);

exit(-1);

}

gettimeofday(&end_timer, NULL);

time_taken = ((end_timer.tv_sec * 1000000 + end_timer.tv_usec) - (start_timer.tv_sec * 1000000 + start_timer.tv_usec));

printf("Time taken by clEnqueueReadBuffer-2 %ld\n", time_taken);

//launching another kernel

err = clEnqueueTask(commandQueue[0], kernel, 0, NULL, &kernel_event[0]);

if (CL_SUCCESS != err) {

printf("Error in clEnqueueTask kernel-1 %d\n\n", err);

exit(-1);

}

int main()

{

for(int i = 0; i < 100; i++)

{

if(i == 0)

function1();

else

function2();

/* processing on cpu */

for(int id = 0; id < 1000; id++)

{

/* processing on cpu */

struct timeval begin_cq, end_cq;

gettimeofday(&begin_cq, NULL);

cl_int res, status;

res = clGetEventInfo(kernel_event[0], CL_EVENT_COMMAND_EXECUTION_STATUS, sizeof(cl_int), &status, NULL);

switch (status)

{

case CL_QUEUED:

printf("Execution Status: Queued\n");

break;

case CL_SUBMITTED:

printf("Execution Status: Submitted\n");

break;

case CL_RUNNING:

printf("Execution Status: Running\n");

break;

case CL_COMPLETE:

printf("Execution Status: Completed\n");

break;

default:

printf("Execution Status: Error (%d)\n", status);

break;

}

clFlush(commandQueue[0]);

gettimeofday(&end_cq, NULL);

long time_taken_cq = ((end_cq.tv_sec * 1000000 + end_cq.tv_usec) - (begin_cq.tv_sec * 1000000 + begin_cq.tv_usec));

printf("Time taken by clFlush %ld micro sec\n", time_taken_cq);

}//for(id)

}//for(i)

return 0;

}

Output:

In function-1

Execution Status: Running

Time taken by clFlush 5 micro sec

Execution Status: Running