linux-kernel - Re: [RFC PATCH] sched: let task migration destination cpu do active balance

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Message-ID: <534F69D8.40605@linaro.org>
Date:	Thu, 17 Apr 2014 13:42:48 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	mingo@...hat.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
	efault@....de, chris.redpath@....com, wangyun@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched: let task migration destination cpu do active
 balance

On 04/16/2014 08:13 PM, Peter Zijlstra wrote:
> On Wed, Apr 16, 2014 at 07:34:29PM +0800, Alex Shi wrote:
>> Chris Redpath found an issue on active balance: 
>> We let the task source cpu, the busiest cpu, do the active balance,
>> while the destination cpu maybe idle. thus we take the busiest cpu
>> time, but left the idlest cpu wait. That is not good for performance.
>>
>> This patch let the destination cpu do active balance. It will give tasks
>> more running time.
>>
>> Signed-off-by: Alex Shi <alex.shi@...aro.org>
>> ---
>>  kernel/sched/fair.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 9b4c4f3..cccee76 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6308,7 +6308,7 @@ more_balance:
>>  			raw_spin_unlock_irqrestore(&busiest->lock, flags);
>>  
>>  			if (active_balance) {
>> -				stop_one_cpu_nowait(cpu_of(busiest),
>> +				stop_one_cpu_nowait(busiest->push_cpu,
>>  					active_load_balance_cpu_stop, busiest,
>>  					&busiest->active_balance_work);
>>  			}
> 
> This doesn't make sense, the whole point of active balance is that we're
> going to move current, for that to work we have to interrupt the CPU
> current is running on and make sure another task (the stopper task in
> this case) is running, so that the previous current is now a !running
> task and we can move it around.
> 

Sure, you are right. thanks for correction!

-- 
Thanks
    Alex
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