util/u_queue: add an option to set the minimum thread priority

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/util/u_queue.c

@@ -147,6 +147,21 @@ util_queue_thread_func(void *input)
       u_thread_setname(name);
    }
 
+   if (queue->flags & UTIL_QUEUE_INIT_USE_MINIMUM_PRIORITY) {
+#if defined(__linux__)
+      struct sched_param sched_param = {0};
+
+      /* The nice() function can only set a maximum of 19.
+       * SCHED_IDLE is the same as nice = 20.
+       *
+       * Note that Linux only allows decreasing the priority. The original
+       * priority can't be restored.
+       */
+      pthread_setschedparam(queue->threads[thread_index], SCHED_IDLE,
+                            &sched_param);
+#endif
+   }
+
    while (1) {
       struct util_queue_job job;
 
@@ -197,13 +212,15 @@ bool
 util_queue_init(struct util_queue *queue,
                 const char *name,
                 unsigned max_jobs,
-                unsigned num_threads)
+                unsigned num_threads,
+                unsigned flags)
 {
    unsigned i;
 
    memset(queue, 0, sizeof(*queue));
    queue->name = name;
    queue->num_threads = num_threads;
+   queue->flags = flags;
    queue->max_jobs = max_jobs;
 
    queue->jobs = (struct util_queue_job*)