linux-kernel - Re: [patch 01/15] sched: (fixlet) dont update shares twice on on

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Date:	Wed, 11 May 2011 10:45:49 +0200
From:	Mike Galbraith <efault@....de>
To:	Paul Turner <pjt@...gle.com>
Cc:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [patch 01/15] sched: (fixlet) dont update shares twice on
 on_rq parent

On Wed, 2011-05-11 at 01:13 -0700, Paul Turner wrote:
> On Wed, May 11, 2011 at 12:55 AM, Hidetoshi Seto
> <seto.hidetoshi@...fujitsu.com> wrote:
> > (2011/05/10 17:32), Mike Galbraith wrote:
> >> On Tue, 2011-05-10 at 16:14 +0900, Hidetoshi Seto wrote:
> >>> This small fixlet can stand alone.
> >>> Peter, how about getting this into git tree first?
> >>
> >> tip 2f36825b176f67e5c5228aa33d828bc39718811f contains the below.
> >>
> >>                 /* Don't dequeue parent if it has other entities besides us */
> >> -               if (cfs_rq->load.weight)
> >> +               if (cfs_rq->load.weight) {
> >> +                       /*
> >> +                        * Bias pick_next to pick a task from this cfs_rq, as
> >> +                        * p is sleeping when it is within its sched_slice.
> >> +                        */
> >> +                       if (task_sleep && parent_entity(se))
> >> +                               set_next_buddy(parent_entity(se));
> >>                         break;
> >> +               }
> >>                 flags |= DEQUEUE_SLEEP;
> >>         }
> >
> > Oh, thanks Mike!
> > It seems that this change in tip is better one.
> >
> > Paul, don't you mind rebasing your patches onto tip/sched/core next time?
> > (...or is there better branch for rebase?)
> >
> 
> I thought I had but apparently I missed this.
> 
> We still need to set se = parent_entity(se) to avoid the pointless
> double update below.
> 
> Will definitely rebase.

Wish I could, wouldn't have 114 other patches just to get evaluation
tree up to speed :)

Index: linux-2.6.32/kernel/sched_fair.c
===================================================================
--- linux-2.6.32.orig/kernel/sched_fair.c
+++ linux-2.6.32/kernel/sched_fair.c
@@ -1308,12 +1308,15 @@ static void dequeue_task_fair(struct rq

                /* Don't dequeue parent if it has other entities besides us */
                if (cfs_rq->load.weight) {
+                       /* Avoid double update below. */
+                       se = parent_entity(se);
+
                        /*
                         * Bias pick_next to pick a task from this cfs_rq, as
                         * p is sleeping when it is within its sched_slice.
                         */
-                       if (task_sleep && parent_entity(se))
-                               set_next_buddy(parent_entity(se));
+                       if (task_sleep && se)
+                               set_next_buddy(se);
                        break;
                }
                flags |= DEQUEUE_SLEEP;


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