linux-kernel - Re: [PATCH 2/2] sched: trigger_load

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Date:	Wed, 12 Sep 2012 15:58:30 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, venki@...gle.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] sched: trigger_load_balance clean up

On 09/12/2012 02:36 AM, Suresh Siddha wrote:

> On Mon, 2012-09-10 at 15:10 +0800, Alex Shi wrote:
>> Remove a redundant check for on_null_domain(cpu), and rerange the code
>> that make it more readable.
> 
> hmm, but we are now doing the on_null_domain() check always,
> irrespective of whether we need the load balance or not.
> 
> do we really need the on_null_domain() check there? What happens if we
> just remove it?


A very very simple try can not show removing causes crash. But as to
RCU details, I don't know. :(

CC to Paul

> 
> thanks,
> suresh
> 
>>
>> Signed-off-by: Alex Shi <alex.shi@...el.com>
>> ---
>>  kernel/sched/fair.c |    8 +++++---
>>  1 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 5bbc4bf..529092d 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -4934,11 +4934,13 @@ static inline int on_null_domain(int cpu)
>>  void trigger_load_balance(struct rq *rq, int cpu)
>>  {
>>  	/* Don't need to rebalance while attached to NULL domain */
>> -	if (time_after_eq(jiffies, rq->next_balance) &&
>> -	    likely(!on_null_domain(cpu)))
>> +	if (unlikely(on_null_domain(cpu)))
>> +		return;
>> +
>> +	if (time_after_eq(jiffies, rq->next_balance))
>>  		raise_softirq(SCHED_SOFTIRQ);
>>  #ifdef CONFIG_NO_HZ
>> -	if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
>> +	if (nohz_kick_needed(rq, cpu))
>>  		nohz_balancer_kick(cpu);
>>  #endif
>>  }
> 
> 


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