linux-kernel - Re: [PATCH] sched: Call update_group_power only for local

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Date:	Thu, 08 Jul 2010 20:16:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Michael Neuling <mikey@...ling.org>
Subject: Re: [PATCH] sched: Call update_group_power only for local_group

On Thu, 2010-07-08 at 10:45 -0700, Suresh Siddha wrote:
> > @@ -2433,7 +2433,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
> >               return;
> >       }
> >  
> > -     update_group_power(sd, this_cpu);
> > +     if (local_group)
> > +             update_group_power(sd, this_cpu);
> 
> if IDLE == CPU_NEWLY_IDLE, then all the cpu's in the local group will do
> this. Also update_group_power() can be done on only on the local cpu,
> i.e., when this_cpu == smp_processor_id() right?

It might make sense to only update_group_power on !CPU_NEWLY_IDLE and
rely on the tick driven cpu_power updates.

No sense in updating them in finer slices I guess.

So how about something like:

---
 kernel/sched_fair.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 9910e1b..2f05679 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2427,14 +2427,14 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 	 * domains. In the newly idle case, we will allow all the cpu's
 	 * to do the newly idle load balance.
 	 */
-	if (idle != CPU_NEWLY_IDLE && local_group &&
-	    balance_cpu != this_cpu) {
-		*balance = 0;
-		return;
+	if (idle != CPU_NEWLY_IDLE && local_group) {
+		if (balance_cpu != this_cpu) {
+			*balance = 0;
+			return;
+		}
+		update_group_power(sd, this_cpu);
 	}
 
-	update_group_power(sd, this_cpu);
-
 	/* Adjust by relative CPU power of the group */
 	sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;
 

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