linux-kernel - Re: [PATCH v3 11/22] sched: consider runnable load average in effective

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Date:	Fri, 11 Jan 2013 11:26:59 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Morten Rasmussen <Morten.Rasmussen@....com>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"bp@...en8.de" <bp@...en8.de>, "pjt@...gle.com" <pjt@...gle.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"efault@....de" <efault@....de>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 11/22] sched: consider runnable load average in effective_load

On 01/10/2013 07:28 PM, Morten Rasmussen wrote:
> On Sat, Jan 05, 2013 at 08:37:40AM +0000, Alex Shi wrote:
>> effective_load calculates the load change as seen from the
>> root_task_group. It needs to multiple cfs_rq's tg_runnable_contrib
>> when we turn to runnable load average balance.
>>
>> Signed-off-by: Alex Shi <alex.shi@...el.com>
>> ---
>>  kernel/sched/fair.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index cab62aa..247d6a8 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -2982,7 +2982,8 @@ static void task_waking_fair(struct task_struct *p)
>>  
>>  #ifdef CONFIG_FAIR_GROUP_SCHED
>>  /*
>> - * effective_load() calculates the load change as seen from the root_task_group
>> + * effective_load() calculates the runnable load average change as seen from
>> + * the root_task_group
>>   *
>>   * Adding load to a group doesn't make a group heavier, but can cause movement
>>   * of group shares between cpus. Assuming the shares were perfectly aligned one
>> @@ -3030,13 +3031,17 @@ static void task_waking_fair(struct task_struct *p)
>>   * Therefore the effective change in loads on CPU 0 would be 5/56 (3/8 - 2/7)
>>   * times the weight of the group. The effect on CPU 1 would be -4/56 (4/8 -
>>   * 4/7) times the weight of the group.
>> + *
>> + * After get effective_load of the load moving, will multiple the cpu own
>> + * cfs_rq's runnable contrib of root_task_group.
>>   */
>>  static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
>>  {
>>  	struct sched_entity *se = tg->se[cpu];
>>  
>>  	if (!tg->parent)	/* the trivial, non-cgroup case */
>> -		return wl;
>> +		return wl * tg->cfs_rq[cpu]->tg_runnable_contrib
>> +						>> NICE_0_SHIFT;
> 
> Why do we need to scale the load of the task (wl) by runnable_contrib
> when the task is in the root task group? Wouldn't the load change still
> just be wl?
> 

Here, wl is the load weight, runnable_contrib engaged the runnable time.
>>  
>>  	for_each_sched_entity(se) {
>>  		long w, W;
>> @@ -3084,7 +3089,7 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
>>  		wg = 0;
>>  	}
>>  
>> -	return wl;
>> +	return wl * tg->cfs_rq[cpu]->tg_runnable_contrib >> NICE_0_SHIFT;
> 
> I believe that effective_load() is only used in wake_affine() to compare
> load scenarios of the same task group. Since the task group is the same
> the effective load is scaled by the same factor and should not make any
> difference?
> 
> Also, in wake_affine() the result of effective_load() is added with
> target_load() which is load.weight of the cpu and not a tracked load
> based on runnable_avg_*/contrib?
> 
> Finally, you have not scaled the result of effective_load() in the
> function used when FAIR_GROUP_SCHED is disabled. Should that be scaled
> too?

it should be, thanks reminder.

the wake up is not good for burst wakeup benchmark. I am thinking to
rewrite this part.

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