linux-kernel - Re: [tip:sched/core] sched/fair: Correct unit of load_above

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Date:	Tue, 31 May 2016 06:35:31 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...nel.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [tip:sched/core] sched/fair: Correct unit of load_above_capacity

On Tue, May 24, 2016 at 04:24:01AM +0800, Yuyang Du wrote:
> On Thu, May 19, 2016 at 04:36:38PM +0100, Morten Rasmussen wrote:
> > 
> > And this is exactly you get with this patch :-) load_above_capacity
> > (through max_pull) is multiplied by the group capacity to compute that
> > actual amount of [load] to remove:
> > 
> > env->imbalance 	= load_above_capacity * busiest->group_capacity /
> > 		 	SCHED_CAPACITY_SCALE
> > 
> > 		= 1*NICE_0_LOAD * 3*SCHED_CAPACITY_SCALE /
> > 			SCHED_CAPACITY_SCALE
> > 
> > 		= 3*NICE_0_LOAD
> > 
> > I don't think we disagree on how it should work :-) Without the capacity
> > scaling in this patch you get: 
> > 
> > env->imbalance = (6*SCHED_CAPACITY_SCALE - 3*SCHED_CAPACITY_SCALE) *
> > 			3*SCHED_CAPACITY_SCALE / SCHED_CAPACITY_SCALE
> > 
> > 		= 9*SCHED_CAPACITY_SCALE
> > 
> > Coming back to Yuyang's question. I think it should be NICE_0_LOAD to
> > ensure that the resulting imbalance has the proper unit [load].
> 
> Sorry, I'm still confused. After this patch, the unit is indeed [load], the
> load same as the weight visible to the user. However, you literally compared
> it with sg_lb_stats's avg_load and load_per_task, which has the unit of
> load_avg, which is scaled_load_down(NICE_0_LOAD). Am I missing something?

Hello?