[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>

3 files changed, 16 insertions, 2 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 2c7a23dde2d8..66aa0b938d6a 100644
--- a/fs/pipe.c
+++ b/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);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8a1fcfe80fc7..ac70f845b5b1 100644
--- a/include/linux/sched.h
+++ b/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)
diff --git a/kernel/sched.c b/kernel/sched.c
index 24eed372d280..6da13bba3e23 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1261,6 +1261,16 @@ out_activate:
         }
 
         /*
+         * 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)
          * don't trigger a preemption, if the woken up task will run on
@@ -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);