Add TASKQ_DYNAMIC feature

Setting the TASKQ_DYNAMIC flag will create a taskq with dynamic
semantics.  Initially only a single worker thread will be created
to service tasks dispatched to the queue.  As additional threads
are needed they will be dynamically spawned up to the max number
specified by 'nthreads'.  When the threads are no longer needed,
because the taskq is empty, they will automatically terminate.

Due to the low cost of creating and destroying threads under Linux
by default new threads and spawned and terminated aggressively.
There are two modules options which can be tuned to adjust this
behavior if needed.

* spl_taskq_thread_sequential - The number of sequential tasks,
without interruption, which needed to be handled by a worker
thread before a new worker thread is spawned.  Default 4.

* spl_taskq_thread_dynamic - Provides the ability to completely
disable the use of dynamic taskqs on the system.  This is provided
for the purposes of debugging and troubleshooting.  Default 1
(enabled).

This behavior is fundamentally consistent with the dynamic taskq
implementation found in both illumos and FreeBSD.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tim Chase <[email protected]>
Closes #458

1 files changed, 106 insertions, 57 deletions

diff --git a/module/splat/splat-taskq.c b/module/splat/splat-taskq.c
index 7d4ad5b69..645bc9145 100644
--- a/module/splat/splat-taskq.c
+++ b/module/splat/splat-taskq.c
@@ -28,6 +28,7 @@
 #include <sys/vmem.h>
 #include <sys/random.h>
 #include <sys/taskq.h>
+#include <sys/time.h>
 #include <sys/timer.h>
 #include <linux/delay.h>
 #include "splat-internal.h"
@@ -75,6 +76,10 @@
 #define SPLAT_TASKQ_TEST10_NAME		"cancel"
 #define SPLAT_TASKQ_TEST10_DESC		"Cancel task execution"
 
+#define SPLAT_TASKQ_TEST11_ID		0x020b
+#define SPLAT_TASKQ_TEST11_NAME		"dynamic"
+#define SPLAT_TASKQ_TEST11_DESC		"Dynamic task queue thread creation"
+
 #define SPLAT_TASKQ_ORDER_MAX		8
 #define SPLAT_TASKQ_DEPTH_MAX		16
 
@@ -1052,21 +1057,15 @@ splat_taskq_test7(struct file *file, void *arg)
 
 	rc = splat_taskq_test7_impl(file, arg, B_FALSE);
 	if (rc)
-		return rc;
+		return (rc);
 
 	rc = splat_taskq_test7_impl(file, arg, B_TRUE);
 
-	return rc;
+	return (rc);
 }
 
-/*
- * Create a taskq with 100 threads and dispatch a huge number of trivial
- * tasks to generate contention on tq->tq_lock.  This test should always
- * pass.  The purpose is to provide a benchmark for measuring the
- * effectiveness of taskq optimizations.
- */
 static void
-splat_taskq_test8_func(void *arg)
+splat_taskq_throughput_func(void *arg)
 {
 	splat_taskq_arg_t *tq_arg = (splat_taskq_arg_t *)arg;
 	ASSERT(tq_arg);
@@ -1074,98 +1073,105 @@ splat_taskq_test8_func(void *arg)
 	atomic_inc(tq_arg->count);
 }
 
-#define TEST8_NUM_TASKS			0x20000
-#define TEST8_THREADS_PER_TASKQ		100
-
 static int
-splat_taskq_test8_common(struct file *file, void *arg, int minalloc,
-                         int maxalloc)
+splat_taskq_throughput(struct file *file, void *arg, const char *name,
+    int nthreads, int minalloc, int maxalloc, int flags, int tasks,
+    struct timespec *delta)
 {
 	taskq_t *tq;
 	taskqid_t id;
 	splat_taskq_arg_t tq_arg;
 	taskq_ent_t **tqes;
 	atomic_t count;
+	struct timespec start, stop;
 	int i, j, rc = 0;
 
-	tqes = vmalloc(sizeof(*tqes) * TEST8_NUM_TASKS);
+	tqes = vmalloc(sizeof (*tqes) * tasks);
 	if (tqes == NULL)
-		return -ENOMEM;
-	memset(tqes, 0, sizeof(*tqes) * TEST8_NUM_TASKS);
-
-	splat_vprint(file, SPLAT_TASKQ_TEST8_NAME,
-		     "Taskq '%s' creating (%d/%d/%d)\n",
-		     SPLAT_TASKQ_TEST8_NAME,
-		     minalloc, maxalloc, TEST8_NUM_TASKS);
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST8_NAME, TEST8_THREADS_PER_TASKQ,
-			       maxclsyspri, minalloc, maxalloc,
-			       TASKQ_PREPOPULATE)) == NULL) {
-		splat_vprint(file, SPLAT_TASKQ_TEST8_NAME,
-		             "Taskq '%s' create failed\n",
-		             SPLAT_TASKQ_TEST8_NAME);
+		return (-ENOMEM);
+
+	memset(tqes, 0, sizeof (*tqes) * tasks);
+
+	splat_vprint(file, name, "Taskq '%s' creating (%d/%d/%d/%d)\n",
+	    name, nthreads, minalloc, maxalloc, tasks);
+	if ((tq = taskq_create(name, nthreads, maxclsyspri,
+	    minalloc, maxalloc, flags)) == NULL) {
+		splat_vprint(file, name, "Taskq '%s' create failed\n", name);
 		rc = -EINVAL;
 		goto out_free;
 	}
 
 	tq_arg.file = file;
-	tq_arg.name = SPLAT_TASKQ_TEST8_NAME;
+	tq_arg.name = name;
 	tq_arg.count = &count;
 	atomic_set(tq_arg.count, 0);
 
-	for (i = 0; i < TEST8_NUM_TASKS; i++) {
-		tqes[i] = kmalloc(sizeof(taskq_ent_t), GFP_KERNEL);
+	getnstimeofday(&start);
+
+	for (i = 0; i < tasks; i++) {
+		tqes[i] = kmalloc(sizeof (taskq_ent_t), GFP_KERNEL);
 		if (tqes[i] == NULL) {
 			rc = -ENOMEM;
 			goto out;
 		}
-		taskq_init_ent(tqes[i]);
-
-		taskq_dispatch_ent(tq, splat_taskq_test8_func,
-				   &tq_arg, TQ_SLEEP, tqes[i]);
 
+		taskq_init_ent(tqes[i]);
+		taskq_dispatch_ent(tq, splat_taskq_throughput_func,
+		    &tq_arg, TQ_SLEEP, tqes[i]);
 		id = tqes[i]->tqent_id;
 
 		if (id == 0) {
-			splat_vprint(file, SPLAT_TASKQ_TEST8_NAME,
-			        "Taskq '%s' function '%s' dispatch "
-				"%d failed\n", tq_arg.name,
-				sym2str(splat_taskq_test8_func), i);
-				rc = -EINVAL;
-				goto out;
+			splat_vprint(file, name, "Taskq '%s' function '%s' "
+			    "dispatch %d failed\n", tq_arg.name,
+			    sym2str(splat_taskq_throughput_func), i);
+			rc = -EINVAL;
+			goto out;
 		}
 	}
 
-	splat_vprint(file, SPLAT_TASKQ_TEST8_NAME, "Taskq '%s' "
-		     "waiting for %d dispatches\n", tq_arg.name,
-		     TEST8_NUM_TASKS);
+	splat_vprint(file, name, "Taskq '%s' waiting for %d dispatches\n",
+	    tq_arg.name, tasks);
+
 	taskq_wait(tq);
-	splat_vprint(file, SPLAT_TASKQ_TEST8_NAME, "Taskq '%s' "
-		     "%d/%d dispatches finished\n", tq_arg.name,
-		     atomic_read(tq_arg.count), TEST8_NUM_TASKS);
 
-	if (atomic_read(tq_arg.count) != TEST8_NUM_TASKS)
+	if (delta != NULL) {
+		getnstimeofday(&stop);
+		*delta = timespec_sub(stop, start);
+	}
+
+	splat_vprint(file, name, "Taskq '%s' %d/%d dispatches finished\n",
+	    tq_arg.name, atomic_read(tq_arg.count), tasks);
+
+	if (atomic_read(tq_arg.count) != tasks)
 		rc = -ERANGE;
 
 out:
-	splat_vprint(file, SPLAT_TASKQ_TEST8_NAME, "Taskq '%s' destroying\n",
-	           tq_arg.name);
+	splat_vprint(file, name, "Taskq '%s' destroying\n", tq_arg.name);
 	taskq_destroy(tq);
 out_free:
-	for (j = 0; j < TEST8_NUM_TASKS && tqes[j] != NULL; j++)
+	for (j = 0; j < tasks && tqes[j] != NULL; j++)
 		kfree(tqes[j]);
+
 	vfree(tqes);
 
-	return rc;
+	return (rc);
 }
 
+/*
+ * Create a taskq with 100 threads and dispatch a huge number of trivial
+ * tasks to generate contention on tq->tq_lock.  This test should always
+ * pass.  The purpose is to provide a benchmark for measuring the
+ * effectiveness of taskq optimizations.
+ */
+#define	TEST8_NUM_TASKS			0x20000
+#define	TEST8_THREADS_PER_TASKQ		100
+
 static int
 splat_taskq_test8(struct file *file, void *arg)
 {
-	int rc;
-
-	rc = splat_taskq_test8_common(file, arg, 1, 100);
-
-	return rc;
+	return (splat_taskq_throughput(file, arg,
+	    SPLAT_TASKQ_TEST8_NAME, TEST8_THREADS_PER_TASKQ,
+	    1, INT_MAX, TASKQ_PREPOPULATE, TEST8_NUM_TASKS, NULL));
 }
 
 /*
@@ -1433,6 +1439,46 @@ out_free:
 	return rc;
 }
 
+/*
+ * Create a dynamic taskq with 100 threads and dispatch a huge number of
+ * trivial tasks.  This will cause the taskq to grow quickly to its max
+ * thread count.  This test should always pass.  The purpose is to provide
+ * a benchmark for measuring the performance of dynamic taskqs.
+ */
+#define	TEST11_NUM_TASKS			100000
+#define	TEST11_THREADS_PER_TASKQ		100
+
+static int
+splat_taskq_test11(struct file *file, void *arg)
+{
+	struct timespec normal, dynamic;
+	int error;
+
+	error = splat_taskq_throughput(file, arg, SPLAT_TASKQ_TEST11_NAME,
+	    TEST11_THREADS_PER_TASKQ, 1, INT_MAX,
+	    TASKQ_PREPOPULATE, TEST11_NUM_TASKS, &normal);
+	if (error)
+		return (error);
+
+	error = splat_taskq_throughput(file, arg, SPLAT_TASKQ_TEST11_NAME,
+	    TEST11_THREADS_PER_TASKQ, 1, INT_MAX,
+	    TASKQ_PREPOPULATE | TASKQ_DYNAMIC, TEST11_NUM_TASKS, &dynamic);
+	if (error)
+		return (error);
+
+	splat_vprint(file, SPLAT_TASKQ_TEST11_NAME,
+	    "Timing taskq_wait(): normal=%ld.%09lds, dynamic=%ld.%09lds\n",
+	    normal.tv_sec, normal.tv_nsec,
+	    dynamic.tv_sec, dynamic.tv_nsec);
+
+	/* A 10x increase in runtime is used to indicate a core problem. */
+	if ((dynamic.tv_sec * NANOSEC + dynamic.tv_nsec) >
+	    ((normal.tv_sec * NANOSEC + normal.tv_nsec) * 10))
+		error = -ETIME;
+
+	return (error);
+}
+
 splat_subsystem_t *
 splat_taskq_init(void)
 {
@@ -1470,6 +1516,8 @@ splat_taskq_init(void)
 	              SPLAT_TASKQ_TEST9_ID, splat_taskq_test9);
 	SPLAT_TEST_INIT(sub, SPLAT_TASKQ_TEST10_NAME, SPLAT_TASKQ_TEST10_DESC,
 	              SPLAT_TASKQ_TEST10_ID, splat_taskq_test10);
+	SPLAT_TEST_INIT(sub, SPLAT_TASKQ_TEST11_NAME, SPLAT_TASKQ_TEST11_DESC,
+	              SPLAT_TASKQ_TEST11_ID, splat_taskq_test11);
 
         return sub;
 }
@@ -1478,6 +1526,7 @@ void
 splat_taskq_fini(splat_subsystem_t *sub)
 {
         ASSERT(sub);
+	SPLAT_TEST_FINI(sub, SPLAT_TASKQ_TEST11_ID);
 	SPLAT_TEST_FINI(sub, SPLAT_TASKQ_TEST10_ID);
 	SPLAT_TEST_FINI(sub, SPLAT_TASKQ_TEST9_ID);
 	SPLAT_TEST_FINI(sub, SPLAT_TASKQ_TEST8_ID);