quoted

quoted

On Fri, Jul 18, 2008 at  8:39 AM, in message <1216384754.28405.31.camel@twins>,

Peter Zijlstra [off-list ref] wrote: 

On Thu, 2008-07-03 at 15:37 -0600, Gregory Haskins wrote:

quoted

commit 62fb185130e4d420f71a30ff59d8b16b74ef5d2b reverted some patches
in the scheduler, but it looks like it may have left a few redundant
calls to inc_load/dec_load remain in set_user_nice (since the
 dequeue_task/enqueue_task take care of the load.  This could result
in the load values being off since the load may change while dequeued.

I just checked out v2.6.25.10 but cannot see dequeue_task() do it.

Perhaps I was trying to hit a moving target, or did not have enough coffee that day ;)

I will look again to see if I made a mistake.

Thanks Peter,

-Greg

deactivate_task() otoh does do it.

static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
{
	p->sched_class->dequeue_task(rq, p, sleep);
	p->se.on_rq = 0;
}

vs

static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep)
{
	if (task_contributes_to_load(p))
		rq->nr_uninterruptible++;

	dequeue_task(rq, p, sleep);
	dec_nr_running(p, rq);
}

where

static void dec_nr_running(struct task_struct *p, struct rq *rq)
{
	rq->nr_running--;
	dec_load(rq, p);
}

And since set_user_nice() actually changes the load we'd better not
forget to do this dec/inc load stuff.

So I'm thinking this patch would actually break stuff.

quoted

Signed-off-by: Gregory Haskins <redacted>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <redacted>
---

 kernel/sched.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 31f91d9..b046754 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c

@@ -4679,10 +4679,8 @@ void set_user_nice(struct task_struct *p, long nice)
 		goto out_unlock;
 	}
 	on_rq = p->se.on_rq;
-	if (on_rq) {
+	if (on_rq)
 		dequeue_task(rq, p, 0);
-		dec_load(rq, p);
-	}
 
 	p->static_prio = NICE_TO_PRIO(nice);
 	set_load_weight(p);

@@ -4692,7 +4690,7 @@ void set_user_nice(struct task_struct *p, long nice)
 
 	if (on_rq) {
 		enqueue_task(rq, p, 0);
-		inc_load(rq, p);
+
 		/*
 		 * If the task increased its priority or is running and
 		 * lowered its priority, then reschedule its CPU:

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