linux-kernel - Re: [git] CFS-devel, group scheduler, fixes

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Date:	Tue, 18 Sep 2007 21:36:30 +0200
From:	dimm <dmitry.adamushko@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [git] CFS-devel, group scheduler, fixes

[ well, don't expect to find here anything like RDCFS
(no, 'D' does not stand for 'dumb'!). I was focused
on more prosaic things in the mean time so just
didn't have time for writing it.. ]

here is a few cleanup/simplification/optimization(s)
based on the recent modifications in the sched-dev tree.

(1) optimize task_new_fair()
(2) simplify yield_task()
(3) rework enqueue/dequeue_entity() to get rid of
sched_class::set_curr_task()

additionally, the changes somewhat decrease code size:

   text    data     bss     dec     hex filename
  43538    5398      48   48984    bf58 build/kernel/sched.o.before
  43250    5390      48   48688    be30 build/kernel/sched.o

(SMP + lots of debugging options but, I guess, in this case the diff
should remain visible for any combination).

---

(1)

due to the fact that we no longer keep the 'current' within the tree,
dequeue/enqueue_entity() is useless for the 'current' in task_new_fair().
We are about to reschedule and sched_class->put_prev_task() will put
the 'current' back into the tree, based on its new key.

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@...il.com>

---
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 6e52d5a..5a244e2 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -969,10 +969,11 @@ static void task_new_fair(struct rq *rq, struct task_struct *p)

 	if (sysctl_sched_child_runs_first &&
 			curr->vruntime < se->vruntime) {
-
-		dequeue_entity(cfs_rq, curr, 0);
+		/*
+ 		 * Upon rescheduling, sched_class::put_prev_task() will place
+ 		 * 'current' within the tree based on its new key value.
+ 		 */
 		swap(curr->vruntime, se->vruntime);
-		enqueue_entity(cfs_rq, curr, 0);
 	}

 	update_stats_enqueue(cfs_rq, se);

---

Dmitry

-
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