[PATCH] sched: TASK_NONINTERACTIVE

This patch implements a task state bit (TASK_NONINTERACTIVE), which can be
used by blocking points to mark the task's wait as "non-interactive".  This
does not mean the task will be considered a CPU-hog - the wait will simply
not have an effect on the waiting task's priority - positive or negative
alike.  Right now only pipe_wait() will make use of it, because it's a
common source of not-so-interactive waits (kernel compilation jobs, etc.).
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/pipe.c

@@ -39,7 +39,11 @@ void pipe_wait(struct inode * inode)
 {
 	DEFINE_WAIT(wait);
 
-	prepare_to_wait(PIPE_WAIT(*inode), &wait, TASK_INTERRUPTIBLE);
+	/*
+	 * Pipes are system-local resources, so sleeping on them
+	 * is considered a noninteractive wait:
+	 */
+	prepare_to_wait(PIPE_WAIT(*inode), &wait, TASK_INTERRUPTIBLE|TASK_NONINTERACTIVE);
 	up(PIPE_SEM(*inode));
 	schedule();
 	finish_wait(PIPE_WAIT(*inode), &wait);

include/linux/sched.h

@@ -114,6 +114,7 @@ extern unsigned long nr_iowait(void);
 #define TASK_TRACED		8
 #define EXIT_ZOMBIE		16
 #define EXIT_DEAD		32
+#define TASK_NONINTERACTIVE	64
 
 #define __set_task_state(tsk, state_value)		\
 	do { (tsk)->state = (state_value); } while (0)

kernel/sched.c

@@ -1260,6 +1260,16 @@ out_activate:
 		p->activated = -1;
 	}
 
+	/*
+	 * Tasks that have marked their sleep as noninteractive get
+	 * woken up without updating their sleep average. (i.e. their
+	 * sleep is handled in a priority-neutral manner, no priority
+	 * boost and no penalty.)
+	 */
+	if (old_state & TASK_NONINTERACTIVE)
+		__activate_task(p, rq);
+	else
+		activate_task(p, rq, cpu == this_cpu);
 	/*
 	 * Sync wakeups (i.e. those types of wakeups where the waker
 	 * has indicated that it will leave the CPU in short order)
@@ -1268,7 +1278,6 @@ out_activate:
 	 * the waker guarantees that the freshly woken up task is going
 	 * to be considered on this CPU.)
 	 */
-	activate_task(p, rq, cpu == this_cpu);
 	if (!sync || cpu != this_cpu) {
 		if (TASK_PREEMPTS_CURR(p, rq))
 			resched_task(rq->curr);