linux-kernel - Re: [PATCH 2/2] sched: Fix next_balance logic in rebalance_domains() and idle

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Date:	Thu, 8 May 2014 20:06:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Low <jason.low2@...com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	daniel.lezcano@...aro.org, alex.shi@...aro.org,
	preeti@...ux.vnet.ibm.com, efault@....de,
	vincent.guittot@...aro.org, morten.rasmussen@....com, aswin@...com
Subject: Re: [PATCH 2/2] sched: Fix next_balance logic in rebalance_domains()
 and idle_balance()

On Thu, May 08, 2014 at 09:59:24AM -0700, Jason Low wrote:
> On Mon, 2014-04-28 at 15:45 -0700, Jason Low wrote:
> > Currently, in idle_balance(), we update rq->next_balance when we pull_tasks. 
> > However, it is also important to update this in the !pulled_tasks case too.
> > 
> > When the CPU is "busy" (the CPU isn't idle), rq->next_balance gets computed
> > using sd->busy_factor (so we increase the balance interval when the CPU is
> > busy). However, when the CPU goes idle, rq->next_balance could still be set
> > to a large value that was computed with the sd->busy_factor.
> > 
> > Thus, we need to also update rq->next_balance in idle_balance() in the cases
> > where !pulled_tasks too, so that rq->next_balance gets updated without taking
> > the busy_factor into account when the CPU is about to go idle.
> > 
> > This patch makes rq->next_balance get updated independently of whether or
> > not we pulled_task. Also, we add logic to ensure that we always traverse
> > at least 1 of the sched domains to get a proper next_balance value for
> > updating rq->next_balance.
> > 
> > Additionally, since load_balance() modifies the sd->balance_interval, we
> > need to re-obtain the sched domain's interval after the call to
> > load_balance() in rebalance_domains() before we update rq->next_balance.
> > 
> > This patch adds and uses 2 new helper functions, update_next_balance() and
> > get_sd_balance_interval() to update next_balance and obtain the sched
> > domain's balance_interval. 
> 
> 
> Hi Peter,
> 
> I noticed that patch 1 is in tip, but not this patch 2. I was wondering
> what the current status with this [PATCH 2/2] is at the moment.

That made a particular .config explode, need to look at it.
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