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

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Date:	Tue, 10 May 2011 10:32:06 +0200
From:	Mike Galbraith <efault@....de>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	Paul Turner <pjt@...gle.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 Tue, 2011-05-10 at 16:14 +0900, Hidetoshi Seto wrote:
> (2011/05/03 18:28), Paul Turner wrote:
> > In dequeue_task_fair() we bail on dequeue when we encounter a parenting entity
> > with additional weight.  However, we perform a double shares update on this
> > entity since we continue the shares update traversal from that point, despite
> > dequeue_entity() having already updated its queuing cfs_rq.
> > 
> > Avoid this by starting from the parent when we resume.
> > 
> > Signed-off-by: Paul Turner <pjt@...gle.com>
> > ---
> >  kernel/sched_fair.c |    4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > Index: tip/kernel/sched_fair.c
> > ===================================================================
> > --- tip.orig/kernel/sched_fair.c
> > +++ tip/kernel/sched_fair.c
> > @@ -1355,8 +1355,10 @@ static void dequeue_task_fair(struct rq 
> >  		dequeue_entity(cfs_rq, se, flags);
> >  
> >  		/* Don't dequeue parent if it has other entities besides us */
> > -		if (cfs_rq->load.weight)
> > +		if (cfs_rq->load.weight) {
> > +			se = parent_entity(se);
> >  			break;
> > +		}
> >  		flags |= DEQUEUE_SLEEP;
> >  	}
> >  
> 
> Reviewed-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
> 
> 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;
        }


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