boot: add kernel boot parameters for kernel thread priorities

Add kernel boot parameters to specify the priorities for the following
kernel threads: kthreadd, irq threads, ksoftirqd, posixcputmr.  Also fix
priority check issue introduced with original version of this commit.

Signed-off-by: Sankara S Muthukrishnan <sankara.m@ni.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Scot Salmon <scot.salmon@ni.com>
Acked-by: Josh Cartwright <josh.cartwright@ni.com>
Acked-by: Jeff Westfahl <jeff.westfahl@ni.com>
Natinst-CAR-ID: 376725
[gratian: drop the change for setting the posixcputmr thread priority;
it was improperly migrated past nilrt/14.0.y/3.2 so it had no effect
and is not currently in use by our kernel boot command line]
Signed-off-by: Gratian Crisan <gratian.crisan@ni.com>

Author: sanmut

kernel/irq/manage.c

@@ -36,6 +36,8 @@ early_param("threadirqs", setup_forced_irqthreads);
 # endif
 #endif
 
+static int irqthread_pri = MAX_USER_RT_PRIO/2;
+
 static void __synchronize_hardirq(struct irq_desc *desc)
 {
 	bool inprogress;
@@ -1076,6 +1078,18 @@ void irq_wake_thread(unsigned int irq, void *dev_id)
 }
 EXPORT_SYMBOL_GPL(irq_wake_thread);
 
+static __init int set_irqthread_pri(char *str)
+{
+	int pri;
+
+	get_option(&str, &pri);
+	if (pri > 0 && pri < MAX_USER_RT_PRIO)
+		irqthread_pri = pri;
+	return 0;
+}
+
+early_param("irqthread_pri", set_irqthread_pri);
+
 static int irq_setup_forced_threading(struct irqaction *new)
 {
 	if (!force_irqthreads)
@@ -1136,9 +1150,8 @@ static int
 setup_irq_thread(struct irqaction *new, unsigned int irq, bool secondary)
 {
 	struct task_struct *t;
-	struct sched_param param = {
-		.sched_priority = MAX_USER_RT_PRIO/2,
-	};
+	struct sched_param param;
+	param.sched_priority = irqthread_pri;
 
 	if (!secondary) {
 		t = kthread_create(irq_thread, new, "irq/%d-%s", irq,

kernel/kthread.c

@@ -23,9 +23,14 @@
 #include <linux/cgroup.h>
 #include <trace/events/sched.h>
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+#include <linux/sched/rt.h>
+#endif
+
 static DEFINE_SPINLOCK(kthread_create_lock);
 static LIST_HEAD(kthread_create_list);
 struct task_struct *kthreadd_task;
+static int kthreadd_pri = -1;
 
 struct kthread_create_info
 {
@@ -546,6 +551,13 @@ int kthreadd(void *unused)
 	set_cpus_allowed_ptr(tsk, cpu_all_mask);
 	set_mems_allowed(node_states[N_MEMORY]);
 
+	if (kthreadd_pri != -1) {
+		struct sched_param param;
+
+		param.sched_priority = kthreadd_pri;
+		sched_setscheduler_nocheck(tsk, SCHED_FIFO, &param);
+	}
+
 	current->flags |= PF_NOFREEZE;
 	cgroup_init_kthreadd();
 
@@ -574,6 +586,18 @@ int kthreadd(void *unused)
 	return 0;
 }
 
+static __init int set_kthreadd_pri(char *str)
+{
+	int pri;
+
+	get_option(&str, &pri);
+	if (pri > 0 && pri < MAX_USER_RT_PRIO)
+		kthreadd_pri = pri;
+	return 0;
+}
+
+early_param("kthreadd_pri", set_kthreadd_pri);
+
 void __kthread_init_worker(struct kthread_worker *worker,
 				const char *name,
 				struct lock_class_key *key)

kernel/softirq.c

@@ -30,6 +30,10 @@
 #include <linux/irq.h>
 #include <linux/sched/types.h>
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+#include <linux/sched/rt.h>
+#endif
+
 #define CREATE_TRACE_POINTS
 #include <trace/events/irq.h>
 
@@ -511,6 +515,7 @@ static void ksoftirqd_set_sched_params(unsigned int cpu) { }
  * On RT we serialize softirq execution with a cpu local lock per softirq
  */
 static DEFINE_PER_CPU(struct local_irq_lock [NR_SOFTIRQS], local_softirq_locks);
+static int ksoftirqd_pri = 1;
 
 void __init softirq_early_init(void)
 {
@@ -754,7 +759,9 @@ static inline void ksoftirqd_set_sched_params(unsigned int cpu)
 
 static inline void ktimer_softirqd_set_sched_params(unsigned int cpu)
 {
-	struct sched_param param = { .sched_priority = 1 };
+	struct sched_param param = {
+			.sched_priority = ksoftirqd_pri
+	};
 
 	sched_setscheduler(current, SCHED_FIFO, &param);
 
@@ -777,6 +784,18 @@ static int ktimer_softirqd_should_run(unsigned int cpu)
 	return current->softirqs_raised;
 }
 
+static __init int set_ksoftirqd_pri(char *str)
+{
+	int pri;
+
+	get_option(&str, &pri);
+	if (pri > 0 && pri < MAX_USER_RT_PRIO)
+		ksoftirqd_pri = pri;
+	return 0;
+}
+
+early_param("ksoftirqd_pri", set_ksoftirqd_pri);
+
 #endif /* PREEMPT_RT_FULL */
 /*
  * Enter an interrupt context.