openmp/runtime/test/tasking/omp_fill_taskqueue.c

   1 // RUN: %libomp-compile && env KMP_ENABLE_TASK_THROTTLING=0 %libomp-run
   2 // RUN: %libomp-compile && env KMP_ENABLE_TASK_THROTTLING=1 %libomp-run
   3
   4 #include<omp.h>
   5 #include<stdlib.h>
   6 #include<string.h>
   7
   8 /**
   9  * Test the task throttling behavior of the runtime.
  10  * Unless OMP_NUM_THREADS is 1, the master thread pushes tasks to its own tasks
  11  * queue until either of the following happens:
  12  *   - the task queue is full, and it starts serializing tasks
  13  *   - all tasks have been pushed, and it can begin execution
  14  * The idea is to create a huge number of tasks which execution are blocked
  15  * until the master thread comes to execute tasks (they need to be blocking,
  16  * otherwise the second thread will start emptying the queue).
  17  * At this point we can check the number of enqueued tasks: iff all tasks have
  18  * been enqueued, then there was no task throttling.
  19  * Otherwise there has been some sort of task throttling.
  20  * If what we detect doesn't match the value of the environment variable, the
  21  * test is failed.
  22  */
  23
  24
  25 #define NUM_TASKS 2000
  26
  27
  28 int main()
  29 {
  30   int i;
  31   int block = 1;
  32   int throttling = strcmp(getenv("KMP_ENABLE_TASK_THROTTLING"), "1") == 0;
  33   int enqueued = 0;
  34   int failed = -1;
  35
  36   #pragma omp parallel num_threads(2)
  37   #pragma omp master
  38   {
  39     for (i = 0; i < NUM_TASKS; i++) {
  40       enqueued++;
  41       #pragma omp task
  42       {
  43         int tid;
  44         tid = omp_get_thread_num();
  45         if (tid == 0) {
  46           // As soon as the master thread starts executing task we should unlock
  47           // all tasks, and detect the test failure if it has not been done yet.
  48           if (failed < 0)
  49             failed = throttling ? enqueued == NUM_TASKS : enqueued < NUM_TASKS;
  50 #pragma omp atomic write
  51           block = 0;
  52         }
  53         int wait = 0;
  54         do {
  55 #pragma omp atomic read
  56           wait = block;
  57         } while (wait);
  58       }
  59     }
  60     block = 0;
  61   }
  62
  63   return failed;
  64 }