[PATCH] clean up maximum priorities

This patch further cleans up and separates the code in an effort to
allow setting (a) a larger maximum real-time priority than default and
(b) a maximum kernel RT priority that is separate than the maximum
priority exported to user-space.

include/linux/init_task.h

@@ -45,8 +45,8 @@
     thread_info:	&init_thread_info,				\
     flags:		0,						\
     lock_depth:		-1,						\
-    prio:		120,						\
-    static_prio:	120,						\
+    prio:		MAX_PRIO-20,					\
+    static_prio:	MAX_PRIO-20,					\
     policy:		SCHED_OTHER,					\
     cpus_allowed:	-1,						\
     mm:			NULL,						\

include/linux/sched.h

@@ -206,6 +206,23 @@ struct signal_struct {
 	spinlock_t		siglock;
 };
 
+/*
+ * Priority of a process goes from 0..MAX_PRIO-1, valid RT
+ * priority is 0..MAX_RT_PRIO-1, and SCHED_OTHER tasks are
+ * in the range MAX_RT_PRIO..MAX_PRIO-1. Priority values
+ * are inverted: lower p->prio value means higher priority.
+ *
+ * The MAX_RT_USER_PRIO value allows the actual maximum
+ * RT priority to be separate from the value exported to
+ * user-space.  This allows kernel threads to set their
+ * priority to a value higher than any user task. Note:
+ * MAX_RT_PRIO must not be smaller than MAX_USER_RT_PRIO.
+ */
+
+#define MAX_USER_RT_PRIO	100
+#define MAX_RT_PRIO		MAX_USER_RT_PRIO
+
+#define MAX_PRIO		(MAX_RT_PRIO + 40)
  
 /*
  * Some day this will be a full-fledged user tracking system..

kernel/sched.c

@@ -23,23 +23,9 @@
 #include <linux/completion.h>
 #include <linux/kernel_stat.h>
 
-/*
- * Priority of a process goes from 0 to 139. The 0-99
- * priority range is allocated to RT tasks, the 100-139
- * range is for SCHED_OTHER tasks. Priority values are
- * inverted: lower p->prio value means higher priority.
- * 
- * MAX_USER_RT_PRIO allows the actual maximum RT priority
- * to be separate from the value exported to user-space.
- * NOTE: MAX_RT_PRIO must not be smaller than MAX_USER_RT_PRIO.
- */
-#define MAX_RT_PRIO		100
-#define MAX_USER_RT_PRIO	100
-#define MAX_PRIO		(MAX_RT_PRIO + 40)
-
 /*
  * Convert user-nice values [ -20 ... 0 ... 19 ]
- * to static priority [ 100 ... 139 (MAX_PRIO-1) ],
+ * to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
  * and back.
  */
 #define NICE_TO_PRIO(nice)	(MAX_RT_PRIO + (nice) + 20)
@@ -1138,8 +1124,8 @@ static int setscheduler(pid_t pid, int policy, struct sched_param *param)
 	}
 	
 	/*
-	 * Valid priorities for SCHED_FIFO and SCHED_RR are 1..99, valid
-	 * priority for SCHED_OTHER is 0.
+	 * Valid priorities for SCHED_FIFO and SCHED_RR are
+	 * 1..MAX_USER_RT_PRIO, valid priority for SCHED_OTHER is 0.
 	 */
 	retval = -EINVAL;
 	if (lp.sched_priority < 0 || lp.sched_priority > MAX_USER_RT_PRIO-1)