[RFC PATCH v2 1/5] sched: get effective policy and rt_prio

[Julien Desfossez <jdesfossez@efficios.com>]

Helper functions to get the effective policy and rt_priority from the
prio and policy values. This is useful in PI situations because these
fields are not updated in the task, only the sched_class is temporarily
modified.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
---
 include/linux/sched.h |  2 ++
 kernel/sched/core.c   | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index af39baf..0c03595 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2594,6 +2594,8 @@ static inline bool is_idle_task(const struct task_struct *p)
 	struct thread_info thread_info;
 	unsigned long stack[THREAD_SIZE/sizeof(long)];
 };
+extern int effective_policy(int policy, int prio);
+extern int effective_rt_prio(int prio);
 
 #ifndef __HAVE_ARCH_KSTACK_END
 static inline int kstack_end(void *addr)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f5f7b3c..f3817b5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -916,6 +916,42 @@ static int effective_prio(struct task_struct *p)
 	return p->prio;
 }
 
+/*
+ * Get the effective policy based on the current prio value.
+ */
+int effective_policy(int policy, int prio)
+{
+	if (dl_prio(prio))
+		return SCHED_DEADLINE;
+
+	/* With RT, the default class is SCHED_FIFO. */
+	if (rt_prio(prio)) {
+		if (policy == SCHED_RR)
+			return SCHED_RR;
+		return SCHED_FIFO;
+	}
+
+	/* With fair, the default class is SCHED_NORMAL. */
+	switch (policy) {
+	case SCHED_NORMAL:
+	case SCHED_IDLE:
+	case SCHED_BATCH:
+		return policy;
+	}
+	return SCHED_NORMAL;
+}
+
+/*
+ * Get the effective rt priority based on the current prio value.
+ */
+int effective_rt_prio(int prio)
+{
+	if (!rt_prio(prio))
+		return 0;
+
+	return MAX_RT_PRIO - 1 - prio;
+}
+
 /**
  * task_curr - is this task currently executing on a CPU?
  * @p: the task in question.
-- 
1.9.1