diff --git a/sys/conf/options b/sys/conf/options
index 5939832650e..883f7aed0af 100644
--- a/sys/conf/options
+++ b/sys/conf/options
@@ -663,6 +663,7 @@ WITNESS_SKIPSPIN	opt_witness.h
 
 # options for ACPI support
 ACPI_DEBUG		opt_acpi.h
+ACPI_MAX_TASKS		opt_acpi.h
 ACPI_MAX_THREADS	opt_acpi.h
 
 # ISA support
diff --git a/sys/dev/acpica/Osd/OsdSchedule.c b/sys/dev/acpica/Osd/OsdSchedule.c
index fa91ed8781e..180c3621dce 100644
--- a/sys/dev/acpica/Osd/OsdSchedule.c
+++ b/sys/dev/acpica/Osd/OsdSchedule.c
@@ -1,6 +1,7 @@
 /*-
  * Copyright (c) 2000 Michael Smith
  * Copyright (c) 2000 BSDi
+ * Copyright (c) 2007-2009 Jung-uk Kim <jkim@FreeBSD.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -51,6 +52,12 @@ __FBSDID("$FreeBSD$");
 #define _COMPONENT	ACPI_OS_SERVICES
 ACPI_MODULE_NAME("SCHEDULE")
 
+/*
+ * Allow the user to tune the maximum number of tasks we may enqueue.
+ */
+static int acpi_max_tasks = ACPI_MAX_TASKS;
+TUNABLE_INT("debug.acpi.max_tasks", &acpi_max_tasks);
+
 /*
  * Allow the user to tune the number of task threads we start.  It seems
  * some systems have problems with increased parallelism.
@@ -64,11 +71,54 @@ struct acpi_task_ctx {
     struct task			at_task;
     ACPI_OSD_EXEC_CALLBACK	at_function;
     void 			*at_context;
+    int				at_flag;
+#define	ACPI_TASK_USED		1
+#define	ACPI_TASK_ENQUEUED	2
 };
 
-TASKQUEUE_DEFINE(acpi, taskqueue_thread_enqueue, &taskqueue_acpi,
-    taskqueue_start_threads(&taskqueue_acpi, acpi_max_threads, PWAIT,
-    "acpi_task"));
+struct taskqueue		*acpi_taskq;
+static struct acpi_task_ctx	*acpi_tasks;
+static int			acpi_task_count;
+static int			acpi_taskq_started;
+
+/*
+ * Preallocate some memory for tasks early enough.
+ * malloc(9) cannot be used with spin lock held.
+ */
+static void
+acpi_task_init(void *arg)
+{
+
+    acpi_tasks = malloc(sizeof(*acpi_tasks) * acpi_max_tasks, M_ACPITASK,
+	M_WAITOK | M_ZERO);
+}
+
+SYSINIT(acpi_tasks, SI_SUB_DRIVERS, SI_ORDER_FIRST, acpi_task_init, NULL);
+
+/*
+ * Initialize ACPI task queue.
+ */
+static void
+acpi_taskq_init(void *arg)
+{
+    int i;
+
+    acpi_taskq = taskqueue_create_fast("acpi_task", M_NOWAIT,
+	&taskqueue_thread_enqueue, &acpi_taskq);
+    taskqueue_start_threads(&acpi_taskq, acpi_max_threads, PWAIT, "acpi_task");
+    if (acpi_task_count > 0) {
+	if (bootverbose)
+	    printf("AcpiOsExecute: enqueue %d pending tasks\n",
+		acpi_task_count);
+	for (i = 0; i < acpi_max_tasks; i++)
+	    if (atomic_cmpset_acq_int(&acpi_tasks[i].at_flag, ACPI_TASK_USED,
+		ACPI_TASK_USED | ACPI_TASK_ENQUEUED))
+		taskqueue_enqueue(acpi_taskq, &acpi_tasks[i].at_task);
+    }
+    acpi_taskq_started = 1;
+}
+
+SYSINIT(acpi_taskq, SI_SUB_CONFIGURE, SI_ORDER_SECOND, acpi_taskq_init, NULL);
 
 /*
  * Bounce through this wrapper function since ACPI-CA doesn't understand
@@ -81,7 +131,44 @@ acpi_task_execute(void *context, int pending)
 
     at = (struct acpi_task_ctx *)context;
     at->at_function(at->at_context);
-    free(at, M_ACPITASK);
+    atomic_clear_int(&at->at_flag, ACPI_TASK_USED | ACPI_TASK_ENQUEUED);
+    acpi_task_count--;
+}
+
+static ACPI_STATUS
+acpi_task_enqueue(int priority, ACPI_OSD_EXEC_CALLBACK Function, void *Context)
+{
+    struct acpi_task_ctx *at;
+    int i;
+
+    for (at = NULL, i = 0; i < acpi_max_tasks; i++)
+	if (atomic_cmpset_acq_int(&acpi_tasks[i].at_flag, 0, ACPI_TASK_USED)) {
+	    at = &acpi_tasks[i];
+	    acpi_task_count++;
+	    break;
+	}
+    if (at == NULL) {
+	printf("AcpiOsExecute: failed to enqueue task, consider increasing "
+	    "the debug.acpi.max_tasks tunable\n");
+	return (AE_NO_MEMORY);
+    }
+
+    TASK_INIT(&at->at_task, priority, acpi_task_execute, at);
+    at->at_function = Function;
+    at->at_context = Context;
+
+    /*
+     * If the task queue is ready, enqueue it now.
+     */
+    if (acpi_taskq_started) {
+	atomic_set_int(&at->at_flag, ACPI_TASK_ENQUEUED);
+	taskqueue_enqueue(acpi_taskq, &at->at_task);
+	return (AE_OK);
+    }
+    if (bootverbose)
+	printf("AcpiOsExecute: task queue not started\n");
+
+    return (AE_OK);
 }
 
 /*
@@ -92,7 +179,6 @@ ACPI_STATUS
 AcpiOsExecute(ACPI_EXECUTE_TYPE Type, ACPI_OSD_EXEC_CALLBACK Function,
     void *Context)
 {
-    struct acpi_task_ctx *at;
     int pri;
 
     ACPI_FUNCTION_TRACE((char *)(uintptr_t)__func__);
@@ -100,12 +186,6 @@ AcpiOsExecute(ACPI_EXECUTE_TYPE Type, ACPI_OSD_EXEC_CALLBACK Function,
     if (Function == NULL)
 	return_ACPI_STATUS (AE_BAD_PARAMETER);
 
-    at = malloc(sizeof(*at), M_ACPITASK, M_NOWAIT);
-    if (at == NULL)
-	return_ACPI_STATUS (AE_NO_MEMORY);
-
-    at->at_function = Function;
-    at->at_context = Context;
     switch (Type) {
     case OSL_GPE_HANDLER:
     case OSL_NOTIFY_HANDLER:
@@ -126,14 +206,10 @@ AcpiOsExecute(ACPI_EXECUTE_TYPE Type, ACPI_OSD_EXEC_CALLBACK Function,
 	pri = 0;
 	break;
     default:
-	free(at, M_ACPITASK);
 	return_ACPI_STATUS (AE_BAD_PARAMETER);
     }
 
-    TASK_INIT(&at->at_task, pri, acpi_task_execute, at);
-    taskqueue_enqueue(taskqueue_acpi, &at->at_task);
-
-    return_ACPI_STATUS (AE_OK);
+    return_ACPI_STATUS (acpi_task_enqueue(pri, Function, Context));
 }
 
 void
diff --git a/sys/dev/acpica/acpivar.h b/sys/dev/acpica/acpivar.h
index ce6a24253d2..43f77abf5b1 100644
--- a/sys/dev/acpica/acpivar.h
+++ b/sys/dev/acpica/acpivar.h
@@ -457,6 +457,11 @@ ACPI_HANDLE	acpi_GetReference(ACPI_HANDLE scope, ACPI_OBJECT *obj);
  */
 #define	ACPI_DEV_BASE_ORDER	10
 
+/* Default maximum number of tasks to enqueue. */
+#ifndef ACPI_MAX_TASKS
+#define	ACPI_MAX_TASKS		32
+#endif
+
 /* Default number of task queue threads to start. */
 #ifndef ACPI_MAX_THREADS
 #define ACPI_MAX_THREADS	3