MINOR: tasks: only visit filled task slots after processing them

process_runnable_tasks() needs to requeue or wake up tasks after
processing them in batches. By only refilling the existing ones, we
avoid revisiting all the queue. The performance gain is measurable
starting with two threads, where the request rate climbs to 657k/s
compared to 644k.

diff --git a/src/task.c b/src/task.c
index 37994a3318f86124f4cd5f78546f386f0ad1674e..3d61f98cfd8a197f36e7bc40cc305ff9dabac9cb 100644 (file)
--- a/src/task.c
+++ b/src/task.c
@@ -188,6 +188,7 @@ void process_runnable_tasks()
        struct eb32sc_node *rq_next;
        struct task *local_tasks[16];
        int local_tasks_count;
+       int final_tasks_count;
        tasks_run_queue_cur = tasks_run_queue; /* keep a copy for reporting */
        nb_tasks_cur = nb_tasks;
        max_processed = tasks_run_queue;
@@ -241,6 +242,7 @@ void process_runnable_tasks()
 
                SPIN_UNLOCK(TASK_RQ_LOCK, &rq_lock);
 
+               final_tasks_count = 0;
                for (i = 0; i < local_tasks_count ; i++) {
                        t = local_tasks[i];
                        /* This is an optimisation to help the processor's branch
@@ -250,24 +252,23 @@ void process_runnable_tasks()
                                t = process_stream(t);
                        else
                                t = t->process(t);
-                       local_tasks[i] = t;
+                       if (t)
+                               local_tasks[final_tasks_count++] = t;
                }
 
                SPIN_LOCK(TASK_RQ_LOCK, &rq_lock);
-               for (i = 0; i < local_tasks_count ; i++) {
+               for (i = 0; i < final_tasks_count ; i++) {
                        t = local_tasks[i];
-                       if (likely(t != NULL)) {
-                               t->state &= ~TASK_RUNNING;
-                               /* If there is a pending state
-                                * we have to wake up the task
-                                * immediatly, else we defer
-                                * it into wait queue
-                                */
-                               if (t->pending_state)
-                                       __task_wakeup(t);
-                               else
-                                       task_queue(t);
-                       }
+                       t->state &= ~TASK_RUNNING;
+                       /* If there is a pending state
+                        * we have to wake up the task
+                        * immediatly, else we defer
+                        * it into wait queue
+                        */
+                       if (t->pending_state)
+                               __task_wakeup(t);
+                       else
+                               task_queue(t);
                }
        } while (max_processed > 0);