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Date:	Wed, 17 Nov 2010 09:17:19 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	Mike Galbraith <efault@....de>
Cc:	Nikhil Rao <ncrao@...gle.com>,
	Rakib Mullick <rakib.mullick@...il.com>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Yan, Zheng Z" <zheng.z.yan@...el.com>
Subject: Re: [performance bug] volanomark regression on 37-rc1



> ---
>  kernel/sched_fair.c |    4 ----
>  1 file changed, 4 deletions(-)
> 
> Index: linux-2.6/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_fair.c
> +++ linux-2.6/kernel/sched_fair.c
> @@ -1758,10 +1758,6 @@ static void pull_task(struct rq *src_rq,
>  	set_task_cpu(p, this_cpu);
>  	activate_task(this_rq, p, 0);
>  	check_preempt_curr(this_rq, p, 0);
> -
> -	/* re-arm NEWIDLE balancing when moving tasks */
> -	src_rq->avg_idle = this_rq->avg_idle = 2*sysctl_sched_migration_cost;
> -	this_rq->idle_stamp = 0;
>  }
>  
>  /*
> 
> 
In the original source (.36 kernel) the rq->idle_stamp is set as zero
after task was pulled to this cpu in load_balance(). Nikhil move this
setting to pull_task(), that has same effect.
I don't know what the details effect of removing idle_stamp setting
instead of recovered it on idle_balance(). :) 

My machines are doing rc2 performance testing. I may try this patch
after testing finish. 

The following is part of Nikhil's old patch. 
===
@@ -3162,10 +3186,8 @@ static void idle_balance(int this_cpu, struct rq
*this_rq)
                interval = msecs_to_jiffies(sd->balance_interval);
                if (time_after(next_balance, sd->last_balance +
interval))
                        next_balance = sd->last_balance + interval;
-               if (pulled_task) {
-                       this_rq->idle_stamp = 0;
+               if (pulled_task)
                        break;
-               }
        }

Regards
Alex



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