[master] 42417e3 Generalize the task queuing code and specifically exempt acceptor tasks from the queue limits.

[Poul-Henning Kamp]

commit 42417e3631559b01f827e1c455c898d7a8a019d6
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Tue Jun 9 20:17:42 2015 +0000

    Generalize the task queuing code and specifically exempt acceptor
    tasks from the queue limits.
    
    Slightly change the queuelimits to be relative to the full complement
    of worker threads in the pool, rather than the count of currently created
    threads, this should drop less traffic during ramp-up, but retain the
    steady-state behaviour.

diff --git a/bin/varnishd/cache/cache_wrk.c b/bin/varnishd/cache/cache_wrk.c
index a76f02b..2337ab9 100644
--- a/bin/varnishd/cache/cache_wrk.c
+++ b/bin/varnishd/cache/cache_wrk.c
@@ -226,12 +226,11 @@ Pool_Task(struct pool *pp, struct pool_task *task, enum task_how how)
 	CHECK_OBJ_NOTNULL(pp, POOL_MAGIC);
 	AN(task);
 	AN(task->func);
+	assert(how >= TASK_QUEUE_FRONT && how <= TASK_QUEUE_BACK);
 
 	Lck_Lock(&pp->mtx);
 
-	/*
-	 * The common case first:  Take an idle thread, do it.
-	 */
+	/* The common case first:  Take an idle thread, do it. */
 
 	wrk = pool_getidleworker(pp);
 	if (wrk != NULL) {
@@ -244,24 +243,16 @@ Pool_Task(struct pool *pp, struct pool_task *task, enum task_how how)
 		return (0);
 	}
 
-	switch (how) {
-	case TASK_QUEUE_FRONT:
-		/* If we have too much in the queue already, refuse. */
-		if (pp->lqueue > cache_param->wthread_queue_limit) {
-			pp->ndropped++;
-			retval = -1;
-		} else {
-			VTAILQ_INSERT_TAIL(&pp->queues[how], task, list);
-			pp->nqueued++;
-			pp->lqueue++;
-		}
-		break;
-	case TASK_QUEUE_BACK:
-		VTAILQ_INSERT_TAIL(&pp->queues[how], task, list);
+	/* Acceptors are not subject to queue limits */
+	if (how == TASK_QUEUE_BACK ||
+	    pp->lqueue < cache_param->wthread_max +
+	    cache_param->wthread_queue_limit + pp->nthr) {
+		pp->nqueued++;
 		pp->lqueue++;
-		break;
-	default:
-		WRONG("Unknown enum task_how");
+		VTAILQ_INSERT_TAIL(&pp->queues[how], task, list);
+	} else {
+		pp->ndropped++;
+		retval = -1;
 	}
 	Lck_Unlock(&pp->mtx);
 	return (retval);