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

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Date:	Tue, 20 May 2014 16:58:48 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Jason Low <jason.low2@...com>,
	Tim Chen <tim.c.chen@...ux.intel.com>
CC:	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>,
	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 05/20/2014 04:51 PM, 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
>> index 9b4c4f3..97132db 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6764,12 +6764,17 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
>>
>>                 rq = cpu_rq(balance_cpu);
>>
>> -               raw_spin_lock_irq(&rq->lock);
>> -               update_rq_clock(rq);
>> -               update_idle_cpu_load(rq);
>> -               raw_spin_unlock_irq(&rq->lock);
>> -
>> -               rebalance_domains(rq, CPU_IDLE);
>> +               /*
>> +                * If time for next balance is due,
>> +                * do the balance.
>> +                */
>> +               if (time_after(jiffies + 1, rq->next_balance)) {
> 
> Hi Tim,
> 
> 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))"?

I was wondering the same.

Everything else gets my

Reviewed-by: Rik van Riel <riel@...hat.com>

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