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Date:      Wed, 16 Oct 2013 09:52:59 +0000 (UTC)
From:      Alexander Motin <mav@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r256613 - head/sys/kern
Message-ID:  <201310160952.r9G9qxmD019496@svn.freebsd.org>
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Author: mav
Date: Wed Oct 16 09:52:59 2013
New Revision: 256613
URL: http://svnweb.freebsd.org/changeset/base/256613

Log:
  MFprojects/camlock r254763:
  Move tq_enqueue() call out of the queue lock for known handlers (actually
  I have found no others in the base system).  This reduces queue lock hold
  time and congestion spinning under active multithreaded enqueuing.

Modified:
  head/sys/kern/subr_taskqueue.c

Modified: head/sys/kern/subr_taskqueue.c
==============================================================================
--- head/sys/kern/subr_taskqueue.c	Wed Oct 16 09:48:23 2013	(r256612)
+++ head/sys/kern/subr_taskqueue.c	Wed Oct 16 09:52:59 2013	(r256613)
@@ -47,6 +47,9 @@ __FBSDID("$FreeBSD$");
 static MALLOC_DEFINE(M_TASKQUEUE, "taskqueue", "Task Queues");
 static void	*taskqueue_giant_ih;
 static void	*taskqueue_ih;
+static void	 taskqueue_fast_enqueue(void *);
+static void	 taskqueue_swi_enqueue(void *);
+static void	 taskqueue_swi_giant_enqueue(void *);
 
 struct taskqueue_busy {
 	struct task	*tb_running;
@@ -70,6 +73,7 @@ struct taskqueue {
 
 #define	TQ_FLAGS_ACTIVE		(1 << 0)
 #define	TQ_FLAGS_BLOCKED	(1 << 1)
+#define	TQ_FLAGS_UNLOCKED_ENQUEUE	(1 << 2)
 
 #define	DT_CALLOUT_ARMED	(1 << 0)
 
@@ -97,7 +101,8 @@ _timeout_task_init(struct taskqueue *que
 {
 
 	TASK_INIT(&timeout_task->t, priority, func, context);
-	callout_init_mtx(&timeout_task->c, &queue->tq_mutex, 0);
+	callout_init_mtx(&timeout_task->c, &queue->tq_mutex,
+	    CALLOUT_RETURNUNLOCKED);
 	timeout_task->q = queue;
 	timeout_task->f = 0;
 }
@@ -128,6 +133,11 @@ _taskqueue_create(const char *name __unu
 	queue->tq_context = context;
 	queue->tq_spin = (mtxflags & MTX_SPIN) != 0;
 	queue->tq_flags |= TQ_FLAGS_ACTIVE;
+	if (enqueue == taskqueue_fast_enqueue ||
+	    enqueue == taskqueue_swi_enqueue ||
+	    enqueue == taskqueue_swi_giant_enqueue ||
+	    enqueue == taskqueue_thread_enqueue)
+		queue->tq_flags |= TQ_FLAGS_UNLOCKED_ENQUEUE;
 	mtx_init(&queue->tq_mutex, mtxname, NULL, mtxflags);
 
 	return queue;
@@ -197,6 +207,7 @@ taskqueue_enqueue_locked(struct taskqueu
 	if (task->ta_pending) {
 		if (task->ta_pending < USHRT_MAX)
 			task->ta_pending++;
+		TQ_UNLOCK(queue);
 		return (0);
 	}
 
@@ -220,8 +231,12 @@ taskqueue_enqueue_locked(struct taskqueu
 	}
 
 	task->ta_pending = 1;
+	if ((queue->tq_flags & TQ_FLAGS_UNLOCKED_ENQUEUE) != 0)
+		TQ_UNLOCK(queue);
 	if ((queue->tq_flags & TQ_FLAGS_BLOCKED) == 0)
 		queue->tq_enqueue(queue->tq_context);
+	if ((queue->tq_flags & TQ_FLAGS_UNLOCKED_ENQUEUE) == 0)
+		TQ_UNLOCK(queue);
 
 	return (0);
 }
@@ -232,7 +247,6 @@ taskqueue_enqueue(struct taskqueue *queu
 
 	TQ_LOCK(queue);
 	res = taskqueue_enqueue_locked(queue, task);
-	TQ_UNLOCK(queue);
 
 	return (res);
 }
@@ -278,8 +292,8 @@ taskqueue_enqueue_timeout(struct taskque
 			callout_reset(&timeout_task->c, ticks,
 			    taskqueue_timeout_func, timeout_task);
 		}
+		TQ_UNLOCK(queue);
 	}
-	TQ_UNLOCK(queue);
 	return (res);
 }
 
@@ -566,7 +580,6 @@ taskqueue_thread_enqueue(void *context)
 	tqp = context;
 	tq = *tqp;
 
-	TQ_ASSERT_LOCKED(tq);
 	wakeup_one(tq);
 }

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