Viewing SCHED_FIFO, SCHED_RR stats in /proc

[Nigel Gamble]

I've just noticed that the priority and nice values listed in
/proc/<pid>/stat aren't very useful for SCHED_FIFO or SCHED_RR tasks.
I'd like to be able to distinguish tasks with these policies from
SCHED_OTHER tasks, and to view task->rt_priority.

Am I correct that this information is not currently available through
/proc?

Here is one way to expose this information that should be compatible
with existing tools like top and ps.  For SCHED_OTHER, the values are
unchanged.  For SCHED_RR and SCHED_FIFO, the priority value displayed is
(20 + task->rt_priority), which distinguishes them for SCHED_OTHER
priorities which can't be greater than 20.  And SCHED_FIFO tasks, whose
nice value is ignored by the scheduler, are distinguished from SCHED_RR
tasks by begin displayed with a nice value of -99.

diff -u -r1.2 array.c
--- linux/fs/proc/array.c	2001/04/16 23:26:41	1.2
+++ linux/fs/proc/array.c	2001/04/26 22:37:56
@@ -336,11 +336,18 @@
 
 	collect_sigign_sigcatch(task, &sigign, &sigcatch);
 
-	/* scale priority and nice values from timeslices to -20..20 */
-	/* to make it look like a "normal" Unix priority/nice value  */
-	priority = task->counter;
-	priority = 20 - (priority * 10 + DEF_COUNTER / 2) / DEF_COUNTER;
-	nice = task->nice;
+	if (task->policy == SCHED_OTHER) {
+		/* scale priority and nice values from timeslices to -20..20 */
+		/* to make it look like a "normal" Unix priority/nice value  */
+		priority = task->counter;
+		priority = 20 - (priority * 10 + DEF_COUNTER / 2) / DEF_COUNTER;
+	} else {
+		priority = 20 + task->rt_priority;
+	}
+	if (task->policy == SCHED_FIFO)
+		nice = -99;
+	else
+		nice = task->nice;
 
 	read_lock(&tasklist_lock);
 	ppid = task->p_opptr->pid;

Can anyone think of a better way of doing this?

Nigel Gamble                                    [e-mail]
Mountain View, CA, USA.                         http://www.nrg.org/

MontaVista Software                             [e-mail]