linux-kernel - Re: [PATCH] sched: Reduce the rate of needless idle load balancing

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Message-ID: <1400690267.2970.287.camel@schen9-DESK>
Date:	Wed, 21 May 2014 09:37:47 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Jason Low <jason.low2@...com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <len.brown@...el.com>, Russ Anderson <rja@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Hedi Berriche <hedi@....com>, Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Reduce the rate of needless idle load balancing

On Tue, 2014-05-20 at 18:15 -0700, Joe Perches wrote:
> On Tue, 2014-05-20 at 14:04 -0700, Tim Chen wrote:
> > On Tue, 2014-05-20 at 13:59 -0700, Tim Chen wrote:
> > > On Tue, 2014-05-20 at 13:51 -0700, Jason Low wrote:
> > > > On Tue, May 20, 2014 at 1:17 PM, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> []
> > > > If we want to do idle load balancing only when it is due for a
> > > > balance, shouldn't the above just be "if (time_after(jiffies,
> > > > rq->next_balance))"?
> > > 
> > > If rq->next_balance and jiffies are equal, then
> > > time_after(jiffies, rq->next_balance) check will be false and
> > > you will not do balance.  But actually you want to balance
> > > for this case so the jiffies+1 was used.
> > 
> > So maybe I should switch the check to 
> > if (time_before(rq->next_balance, jiffies))
> 
> time_after_eq() or time_is_after_eq_jiffies()
> 
> 

I prefer time_after_eq to keep the code style consistent with the
rest of the code in fair.c.

Tim

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