1 files changed, 47 insertions, 0 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0208b71bef80..40d3939b0520 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5124,6 +5124,8 @@ static int _sched_setscheduler(struct task_struct *p, int policy,
  * @policy: new policy.
  * @param: structure containing the new RT priority.
  *
+ * Use sched_set_fifo(), read its comment.
+ *
  * Return: 0 on success. An error code otherwise.
  *
  * NOTE that the task may be already dead.
@@ -5166,6 +5168,51 @@ int sched_setscheduler_nocheck(struct task_struct *p, int policy,
 }
 EXPORT_SYMBOL_GPL(sched_setscheduler_nocheck);
 
+/*
+ * SCHED_FIFO is a broken scheduler model; that is, it is fundamentally
+ * incapable of resource management, which is the one thing an OS really should
+ * be doing.
+ *
+ * This is of course the reason it is limited to privileged users only.
+ *
+ * Worse still; it is fundamentally impossible to compose static priority
+ * workloads. You cannot take two correctly working static prio workloads
+ * and smash them together and still expect them to work.
+ *
+ * For this reason 'all' FIFO tasks the kernel creates are basically at:
+ *
+ *   MAX_RT_PRIO / 2
+ *
+ * The administrator _MUST_ configure the system, the kernel simply doesn't
+ * know enough information to make a sensible choice.
+ */
+int sched_set_fifo(struct task_struct *p)
+{
+	struct sched_param sp = { .sched_priority = MAX_RT_PRIO / 2 };
+	return sched_setscheduler_nocheck(p, SCHED_FIFO, &sp);
+}
+EXPORT_SYMBOL_GPL(sched_set_fifo);
+
+/*
+ * For when you don't much care about FIFO, but want to be above SCHED_NORMAL.
+ */
+int sched_set_fifo_low(struct task_struct *p)
+{
+	struct sched_param sp = { .sched_priority = 1 };
+	return sched_setscheduler_nocheck(p, SCHED_FIFO, &sp);
+}
+EXPORT_SYMBOL_GPL(sched_set_fifo_low);
+
+int sched_set_normal(struct task_struct *p, int nice)
+{
+	struct sched_attr attr = {
+		.sched_policy = SCHED_NORMAL,
+		.sched_nice = nice,
+	};
+	return sched_setattr_nocheck(p, &attr);
+}
+EXPORT_SYMBOL_GPL(sched_set_normal);
+
 static int
 do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
 {