linux-kernel - Re: [PATCH 1/3] sched, balancing: Update rq->max_idle_balance_cost whenever newidle balance is attempted

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Date:	Thu, 24 Apr 2014 19:29:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Low <jason.low2@...com>
Cc:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org,
	alex.shi@...aro.org, efault@....de, vincent.guittot@...aro.org,
	morten.rasmussen@....com, aswin@...com, chegu_vinod@...com
Subject: Re: [PATCH 1/3] sched, balancing: Update rq->max_idle_balance_cost
 whenever newidle balance is attempted

On Thu, Apr 24, 2014 at 07:14:53PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 24, 2014 at 09:53:37AM -0700, Jason Low wrote:
> > 
> > So I thought that the original rationale (commit 1bd77f2d) behind
> > updating rq->next_balance in idle_balance() is that, if we are going
> > idle (!pulled_task), we want to ensure that the next_balance gets
> > calculated without the busy_factor.
> > 
> > If the rq is busy, then rq->next_balance gets updated based on
> > sd->interval * busy_factor. However, when the rq goes from "busy"
> > to idle, rq->next_balance might still have been calculated under
> > the assumption that the rq is busy. Thus, if we are going idle, we
> > would then properly update next_balance without the busy factor
> > if we update when !pulled_task.
> > 
> 
> Its late here and I'm confused!
> 
> So the for_each_domain() loop calculates a new next_balance based on
> ->balance_interval (which has that busy_factor on, right).

Not right, ->balance_interval is the base interval. rebalance_domains()
doesn't update it.

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