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

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Date:	Thu, 08 Jul 2010 14:53:34 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 11:16 -0700, Peter Zijlstra wrote:
> 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;
>  

I am ok with this patch (barring the currently broken aperf/mperf part).

Acked-by: Suresh Siddha <suresh.b.siddha@...el.com>

Also, looking at all this, don't we need to do something like this in
the nohz load balance?

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 9910e1b..ae750e9 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3598,6 +3598,7 @@ static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
 		}
 
 		raw_spin_lock_irq(&this_rq->lock);
+		update_rq_clock(this_rq);
 		update_cpu_load(this_rq);
 		raw_spin_unlock_irq(&this_rq->lock);
 


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