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Message-ID: <1400634953.26709.42.camel@joe-AO725>
Subject: Re: [PATCH] sched: Reduce the rate of needless idle load balancing
From: Joe Perches <joe@perches.com>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Jason Low <jason.low2@hp.com>, Ingo Molnar <mingo@elte.hu>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Len Brown <len.brown@intel.com>, Russ Anderson <rja@sgi.com>,
        Dimitri Sivanich <sivanich@sgi.com>, Hedi Berriche <hedi@sgi.com>,
        Andi Kleen <andi@firstfloor.org>,
        Michel Lespinasse <walken@google.com>, Rik van Riel <riel@redhat.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Date: Tue, 20 May 2014 18:15:53 -0700
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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@linux.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()