Add defclsyspri macro

Add a new defclsyspri macro which can be used to request the default
Linux scheduler priority.  Neither the minclsyspri or maxclsyspri map
to the default Linux kernel thread priority.  This makes it awkward to
create taskqs which run with the same priority as the rest of the kernel
threads on the system which can lead to performance issues.

All SPL callers which previously used minclsyspri or maxclsyspri have
been changed to use defclsyspri.  The vast majority of callers were
part of the test suite which won't have an external impact.  The few
places where it could impact performance the change was from maxclsyspri
to defclsyspri.  This makes it more likely the process will be scheduled
which may help performance.

To facilitate further performance analysis the spl_taskq_thread_priority
module option has been added.  When disabled (0) all newly created kernel
threads will use the default kernel thread priority.  When enabled (1)
the specified taskq priority will be used.  By default this value is
enabled (1).

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

include/sys/sysmacros.h

@@ -95,6 +95,7 @@
  */
 #define minclsyspri			(MAX_RT_PRIO)
 #define maxclsyspri			(MAX_PRIO-1)
+#define defclsyspri			(DEFAULT_PRIO)
 
 #ifndef NICE_TO_PRIO
 #define NICE_TO_PRIO(nice)		(MAX_RT_PRIO + (nice) + 20)

include/sys/taskq.h

@@ -129,7 +129,7 @@ extern int taskq_member(taskq_t *, void *);
 #define taskq_create_proc(name, nthreads, pri, min, max, proc, flags) \
     taskq_create(name, nthreads, pri, min, max, flags)
 #define taskq_create_sysdc(name, nthreads, min, max, proc, dc, flags) \
-    taskq_create(name, nthreads, maxclsyspri, min, max, flags)
+    taskq_create(name, nthreads, defclsyspri, min, max, flags)
 
 int spl_taskq_init(void);
 void spl_taskq_fini(void);

man/man5/spl-module-parameters.5

@@ -266,6 +266,21 @@ aid performance analysis or troubleshooting.
 Default value: \fB1\fR
 .RE
 
+.sp
+.ne 2
+.na
+\fBspl_taskq_thread_priority\fR (int)
+.ad
+.RS 12n
+Allow newly created taskq threads to set a non-default scheduler priority.
+When enabled the priority specified when a taskq is created will be applied
+to all threads created by that taskq.  When disabled all threads will use
+the default Linux kernel thread priority.  By default, this behavior is
+enabled.
+.sp
+Default value: \fB1\fR
+.RE
+
 .sp
 .ne 2
 .na

module/spl/spl-kmem-cache.c

@@ -1725,7 +1725,7 @@ spl_kmem_cache_init(void)
 	init_rwsem(&spl_kmem_cache_sem);
 	INIT_LIST_HEAD(&spl_kmem_cache_list);
 	spl_kmem_cache_taskq = taskq_create("spl_kmem_cache",
-	    spl_kmem_cache_kmem_threads, maxclsyspri,
+	    spl_kmem_cache_kmem_threads, defclsyspri,
 	    spl_kmem_cache_kmem_threads * 8, INT_MAX,
 	    TASKQ_PREPOPULATE | TASKQ_DYNAMIC);
 	spl_register_shrinker(&spl_kmem_cache_shrinker);

module/spl/spl-taskq.c

@@ -36,6 +36,11 @@ int spl_taskq_thread_dynamic = 1;
 module_param(spl_taskq_thread_dynamic, int, 0644);
 MODULE_PARM_DESC(spl_taskq_thread_dynamic, "Allow dynamic taskq threads");
 
+int spl_taskq_thread_priority = 1;
+module_param(spl_taskq_thread_priority, int, 0644);
+MODULE_PARM_DESC(spl_taskq_thread_priority,
+    "Allow non-default priority for taskq threads");
+
 int spl_taskq_thread_sequential = 4;
 module_param(spl_taskq_thread_sequential, int, 0644);
 MODULE_PARM_DESC(spl_taskq_thread_sequential,
@@ -913,7 +918,9 @@ taskq_thread_create(taskq_t *tq)
 		kthread_bind(tqt->tqt_thread, last_used_cpu);
 	}
 
-	set_user_nice(tqt->tqt_thread, PRIO_TO_NICE(tq->tq_pri));
+	if (spl_taskq_thread_priority)
+		set_user_nice(tqt->tqt_thread, PRIO_TO_NICE(tq->tq_pri));
+
 	wake_up_process(tqt->tqt_thread);
 
 	return (tqt);
@@ -1070,12 +1077,12 @@ int
 spl_taskq_init(void)
 {
 	system_taskq = taskq_create("spl_system_taskq", MAX(boot_ncpus, 64),
-	    minclsyspri, boot_ncpus, INT_MAX, TASKQ_PREPOPULATE|TASKQ_DYNAMIC);
+	    defclsyspri, boot_ncpus, INT_MAX, TASKQ_PREPOPULATE|TASKQ_DYNAMIC);
 	if (system_taskq == NULL)
 		return (1);
 
 	dynamic_taskq = taskq_create("spl_dynamic_taskq", 1,
-	    minclsyspri, boot_ncpus, INT_MAX, TASKQ_PREPOPULATE);
+	    defclsyspri, boot_ncpus, INT_MAX, TASKQ_PREPOPULATE);
 	if (dynamic_taskq == NULL) {
 		taskq_destroy(system_taskq);
 		return (1);

module/splat/splat-atomic.c

@@ -156,7 +156,7 @@ splat_atomic_test1(struct file *file, void *arg)
 
 		thr = (kthread_t *)thread_create(NULL, 0, splat_atomic_work,
 						 &ap, 0, &p0, TS_RUN,
-						 minclsyspri);
+						 defclsyspri);
 		if (thr == NULL) {
 			rc = -ESRCH;
 			mutex_exit(&ap.ap_lock);

module/splat/splat-kmem.c

@@ -739,7 +739,7 @@ splat_kmem_cache_thread_test(struct file *file, void *arg, char *name,
 	for (i = 0; i < SPLAT_KMEM_THREADS; i++) {
 		thr = thread_create(NULL, 0,
 				    splat_kmem_cache_test_thread,
-				    kcp, 0, &p0, TS_RUN, minclsyspri);
+				    kcp, 0, &p0, TS_RUN, defclsyspri);
 		if (thr == NULL) {
 			rc = -ESRCH;
 			goto out_cache;

module/splat/splat-mutex.c

@@ -87,7 +87,7 @@ splat_mutex_test1(struct file *file, void *arg)
         if (mp == NULL)
                 return -ENOMEM;
 
-        tq = taskq_create(SPLAT_MUTEX_TEST_TASKQ, 1, maxclsyspri,
+        tq = taskq_create(SPLAT_MUTEX_TEST_TASKQ, 1, defclsyspri,
                           50, INT_MAX, TASKQ_PREPOPULATE);
         if (tq == NULL) {
                 rc = -ENOMEM;
@@ -196,7 +196,7 @@ splat_mutex_test2(struct file *file, void *arg)
 
         /* Create several threads allowing tasks to race with each other */
         tq = taskq_create(SPLAT_MUTEX_TEST_TASKQ, num_online_cpus(),
-                          maxclsyspri, 50, INT_MAX, TASKQ_PREPOPULATE);
+                          defclsyspri, 50, INT_MAX, TASKQ_PREPOPULATE);
         if (tq == NULL) {
                 rc = -ENOMEM;
                 goto out;
@@ -266,7 +266,7 @@ splat_mutex_test3(struct file *file, void *arg)
         mp.mp_file = file;
         mutex_init(&mp.mp_mtx, SPLAT_MUTEX_TEST_NAME, MUTEX_DEFAULT, NULL);
 
-        if ((tq = taskq_create(SPLAT_MUTEX_TEST_NAME, 1, maxclsyspri,
+        if ((tq = taskq_create(SPLAT_MUTEX_TEST_NAME, 1, defclsyspri,
                                50, INT_MAX, TASKQ_PREPOPULATE)) == NULL) {
                 splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Taskq '%s' "
                              "create failed\n", SPLAT_MUTEX_TEST3_NAME);

module/splat/splat-rwlock.c

@@ -327,7 +327,7 @@ splat_rwlock_test2(struct file *file, void *arg)
 
 	/* Create several threads allowing tasks to race with each other */
 	tq = taskq_create(SPLAT_RWLOCK_TEST_TASKQ, num_online_cpus(),
-			  maxclsyspri, 50, INT_MAX, TASKQ_PREPOPULATE);
+			  defclsyspri, 50, INT_MAX, TASKQ_PREPOPULATE);
 	if (tq == NULL) {
 		rc = -ENOMEM;
 		goto out;
@@ -500,7 +500,7 @@ splat_rwlock_test4(struct file *file, void *arg)
 	if (rwp == NULL)
 		return -ENOMEM;
 
-	tq = taskq_create(SPLAT_RWLOCK_TEST_TASKQ, 1, maxclsyspri,
+	tq = taskq_create(SPLAT_RWLOCK_TEST_TASKQ, 1, defclsyspri,
 			  50, INT_MAX, TASKQ_PREPOPULATE);
 	if (tq == NULL) {
 		rc = -ENOMEM;

module/splat/splat-taskq.c

@@ -134,7 +134,7 @@ splat_taskq_test1_impl(struct file *file, void *arg, boolean_t prealloc)
 		     "Taskq '%s' creating (%s dispatch)\n",
 	             SPLAT_TASKQ_TEST1_NAME,
 		     prealloc ? "prealloc" : "dynamic");
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST1_NAME, 1, maxclsyspri,
+	if ((tq = taskq_create(SPLAT_TASKQ_TEST1_NAME, 1, defclsyspri,
 			       50, INT_MAX, TASKQ_PREPOPULATE)) == NULL) {
 		splat_vprint(file, SPLAT_TASKQ_TEST1_NAME,
 		           "Taskq '%s' create failed\n",
@@ -269,7 +269,7 @@ splat_taskq_test2_impl(struct file *file, void *arg, boolean_t prealloc) {
 			     prealloc ? "prealloc" : "dynamic");
 		if ((tq[i] = taskq_create(SPLAT_TASKQ_TEST2_NAME,
 			                  TEST2_THREADS_PER_TASKQ,
-					  maxclsyspri, 50, INT_MAX,
+					  defclsyspri, 50, INT_MAX,
 					  TASKQ_PREPOPULATE)) == NULL) {
 			splat_vprint(file, SPLAT_TASKQ_TEST2_NAME,
 			           "Taskq '%s/%d' create failed\n",
@@ -494,7 +494,7 @@ splat_taskq_test4_common(struct file *file, void *arg, int minalloc,
 		     SPLAT_TASKQ_TEST4_NAME,
 		     prealloc ? "prealloc" : "dynamic",
 		     minalloc, maxalloc, nr_tasks);
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST4_NAME, 1, maxclsyspri,
+	if ((tq = taskq_create(SPLAT_TASKQ_TEST4_NAME, 1, defclsyspri,
 		               minalloc, maxalloc, TASKQ_PREPOPULATE)) == NULL) {
 		splat_vprint(file, SPLAT_TASKQ_TEST4_NAME,
 		             "Taskq '%s' create failed\n",
@@ -712,7 +712,7 @@ splat_taskq_test5_impl(struct file *file, void *arg, boolean_t prealloc)
 		     "Taskq '%s' creating (%s dispatch)\n",
 		     SPLAT_TASKQ_TEST5_NAME,
 		     prealloc ? "prealloc" : "dynamic");
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST5_NAME, 3, maxclsyspri,
+	if ((tq = taskq_create(SPLAT_TASKQ_TEST5_NAME, 3, defclsyspri,
 		               50, INT_MAX, TASKQ_PREPOPULATE)) == NULL) {
 		splat_vprint(file, SPLAT_TASKQ_TEST5_NAME,
 		             "Taskq '%s' create failed\n",
@@ -873,7 +873,7 @@ splat_taskq_test6_impl(struct file *file, void *arg, boolean_t prealloc)
 		     "Taskq '%s' creating (%s dispatch)\n",
 		     SPLAT_TASKQ_TEST6_NAME,
 		     prealloc ? "prealloc" : "dynamic");
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST6_NAME, 3, maxclsyspri,
+	if ((tq = taskq_create(SPLAT_TASKQ_TEST6_NAME, 3, defclsyspri,
 		               50, INT_MAX, TASKQ_PREPOPULATE)) == NULL) {
 		splat_vprint(file, SPLAT_TASKQ_TEST6_NAME,
 		             "Taskq '%s' create failed\n",
@@ -1005,7 +1005,7 @@ splat_taskq_test7_impl(struct file *file, void *arg, boolean_t prealloc)
 	             "Taskq '%s' creating (%s dispatch)\n",
 	             SPLAT_TASKQ_TEST7_NAME,
 	             prealloc ? "prealloc" :  "dynamic");
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST7_NAME, 1, maxclsyspri,
+	if ((tq = taskq_create(SPLAT_TASKQ_TEST7_NAME, 1, defclsyspri,
 	                       50, INT_MAX, TASKQ_PREPOPULATE)) == NULL) {
 		splat_vprint(file, SPLAT_TASKQ_TEST7_NAME,
 		             "Taskq '%s' create failed\n",
@@ -1094,7 +1094,7 @@ splat_taskq_throughput(struct file *file, void *arg, const char *name,
 
 	splat_vprint(file, name, "Taskq '%s' creating (%d/%d/%d/%d)\n",
 	    name, nthreads, minalloc, maxalloc, tasks);
-	if ((tq = taskq_create(name, nthreads, maxclsyspri,
+	if ((tq = taskq_create(name, nthreads, defclsyspri,
 	    minalloc, maxalloc, flags)) == NULL) {
 		splat_vprint(file, name, "Taskq '%s' create failed\n", name);
 		rc = -EINVAL;
@@ -1203,7 +1203,7 @@ splat_taskq_test9(struct file *file, void *arg)
 	splat_vprint(file, SPLAT_TASKQ_TEST9_NAME,
 	    "Taskq '%s' creating (%s dispatch) (%d/%d/%d)\n",
 	    SPLAT_TASKQ_TEST9_NAME, "delay", minalloc, maxalloc, nr_tasks);
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST9_NAME, 3, maxclsyspri,
+	if ((tq = taskq_create(SPLAT_TASKQ_TEST9_NAME, 3, defclsyspri,
 	    minalloc, maxalloc, TASKQ_PREPOPULATE)) == NULL) {
 		splat_vprint(file, SPLAT_TASKQ_TEST9_NAME,
 		    "Taskq '%s' create failed\n", SPLAT_TASKQ_TEST9_NAME);
@@ -1303,7 +1303,7 @@ splat_taskq_test10(struct file *file, void *arg)
 	splat_vprint(file, SPLAT_TASKQ_TEST10_NAME,
 	    "Taskq '%s' creating (%s dispatch) (%d/%d/%d)\n",
 	    SPLAT_TASKQ_TEST10_NAME, "delay", minalloc, maxalloc, nr_tasks);
-	if ((tq = taskq_create(SPLAT_TASKQ_TEST10_NAME, 3, maxclsyspri,
+	if ((tq = taskq_create(SPLAT_TASKQ_TEST10_NAME, 3, defclsyspri,
 	    minalloc, maxalloc, TASKQ_PREPOPULATE)) == NULL) {
 		splat_vprint(file, SPLAT_TASKQ_TEST10_NAME,
 		    "Taskq '%s' create failed\n", SPLAT_TASKQ_TEST10_NAME);

module/splat/splat-thread.c

@@ -112,7 +112,7 @@ splat_thread_test1(struct file *file, void *arg)
 	tp.tp_rc = 0;
 
 	thr = (kthread_t *)thread_create(NULL, 0, splat_thread_work1, &tp, 0,
-			                 &p0, TS_RUN, minclsyspri);
+			                 &p0, TS_RUN, defclsyspri);
 	/* Must never fail under Solaris, but we check anyway since this
 	 * can happen in the linux SPL, we may want to change this behavior */
 	if (thr == NULL)
@@ -161,7 +161,7 @@ splat_thread_test2(struct file *file, void *arg)
 	tp.tp_rc = 0;
 
 	thr = (kthread_t *)thread_create(NULL, 0, splat_thread_work2, &tp, 0,
-			                 &p0, TS_RUN, minclsyspri);
+			                 &p0, TS_RUN, defclsyspri);
 	/* Must never fail under Solaris, but we check anyway since this
 	 * can happen in the linux SPL, we may want to change this behavior */
 	if (thr == NULL)
@@ -278,7 +278,7 @@ splat_thread_test3(struct file *file, void *arg)
 	/* Start tsd wait threads */
 	for (i = 0; i < SPLAT_THREAD_TEST_THREADS; i++) {
 		if (thread_create(NULL, 0, splat_thread_work3_wait,
-				  &tp, 0, &p0, TS_RUN, minclsyspri))
+				  &tp, 0, &p0, TS_RUN, defclsyspri))
 			wait_count++;
 	}
 
@@ -295,7 +295,7 @@ splat_thread_test3(struct file *file, void *arg)
 	/* Start tsd exit threads */
 	for (i = 0; i < SPLAT_THREAD_TEST_THREADS; i++) {
 		if (thread_create(NULL, 0, splat_thread_work3_exit,
-				  &tp, 0, &p0, TS_RUN, minclsyspri))
+				  &tp, 0, &p0, TS_RUN, defclsyspri))
 			exit_count++;
 	}