linux-kernel - Re: [PATCH v5 7/7] sched: consider runnable load average in effective

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Date:	Mon, 06 May 2013 15:20:36 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
CC:	Alex Shi <alex.shi@...el.com>, mingo@...hat.com,
	peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, morten.rasmussen@....com,
	vincent.guittot@...aro.org, viresh.kumar@...aro.org,
	linux-kernel@...r.kernel.org, mgorman@...e.de, riel@...hat.com
Subject: Re: [PATCH v5 7/7] sched: consider runnable load average in effective_load

Hi, Preeti

On 05/06/2013 03:10 PM, Preeti U Murthy wrote:
> Hi Alex,Michael,
> 
> Can you try out the below patch and check?

Sure, I will take a try also.

I have the reason mentioned in the changelog.
> If this also causes performance regression,you probably need to remove changes made in 
> effective_load() as Michael points out. I believe the below patch should not cause 
> performance regression.

Actually according to the current results of Alex's suggestion, I think
the issue already addressed, anyway, I will test this patch and reply
them at all, let's choose the best way later ;-)

Regards,
Michael Wang

> 
> The below patch is a substitute for patch 7.
> 
> 
> -------------------------------------------------------------------------------
> 
> sched: Modify effective_load() to use runnable load average
> 
> From: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> 
> The runqueue weight distribution should update the runnable load average of
> the cfs_rq on which the task will be woken up.
> 
> However since the computation of se->load.weight takes into consideration
> the runnable load average in update_cfs_shares(),no need to modify this in
> effective_load().
> ---
>  kernel/sched/fair.c |    9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 790e23d..5489022 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3045,7 +3045,7 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
>  		/*
>  		 * w = rw_i + @wl
>  		 */
> -		w = se->my_q->load.weight + wl;
> +		w = se->my_q->runnable_load_avg + wl;
> 
>  		/*
>  		 * wl = S * s'_i; see (2)
> @@ -3066,6 +3066,9 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
>  		/*
>  		 * wl = dw_i = S * (s'_i - s_i); see (3)
>  		 */
> +		/* Do not modify the below as it already contains runnable
> +		 * load average in its computation
> +		 */
>  		wl -= se->load.weight;
> 
>  		/*
> @@ -3112,14 +3115,14 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
>  	 */
>  	if (sync) {
>  		tg = task_group(current);
> -		weight = current->se.load.weight;
> +		weight = current->se.avg.load_avg_contrib;
> 
>  		this_load += effective_load(tg, this_cpu, -weight, -weight);
>  		load += effective_load(tg, prev_cpu, 0, -weight);
>  	}
> 
>  	tg = task_group(p);
> -	weight = p->se.load.weight;
> +	weight = p->se.avg.load_avg_contrib;
> 
>  	/*
>  	 * In low-load situations, where prev_cpu is idle and this_cpu is idle
> 
> 
> Regards
> Preeti U Murthy
> 
> On 05/06/2013 09:04 AM, Michael Wang wrote:
>> Hi, Alex
>>
>> On 05/06/2013 09:45 AM, Alex Shi wrote:
>>> effective_load calculates the load change as seen from the
>>> root_task_group. It needs to engage the runnable average
>>> of changed task.
>> [snip]
>>>   */
>>> @@ -3045,7 +3045,7 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
>>>  		/*
>>>  		 * w = rw_i + @wl
>>>  		 */
>>> -		w = se->my_q->load.weight + wl;
>>> +		w = se->my_q->tg_load_contrib + wl;
>>
>> I've tested the patch set, seems like the last patch caused big
>> regression on pgbench:
>>
>> 			base	patch 1~6	patch 1~7
>> | db_size | clients |  tps  |   |  tps  |	|  tps  |
>> +---------+---------+-------+	+-------+	+-------+
>> | 22 MB   |      32 | 43420 |	| 53387 |	| 41625 |
>>
>> I guess some magic thing happened in effective_load() while calculating
>> group decay combined with load decay, what's your opinion?
>>
>> Regards,
>> Michael Wang
>>
>>>
>>>  		/*
>>>  		 * wl = S * s'_i; see (2)
>>> @@ -3066,7 +3066,7 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
>>>  		/*
>>>  		 * wl = dw_i = S * (s'_i - s_i); see (3)
>>>  		 */
>>> -		wl -= se->load.weight;
>>> +		wl -= se->avg.load_avg_contrib;
>>>
>>>  		/*
>>>  		 * Recursively apply this logic to all parent groups to compute
>>> @@ -3112,14 +3112,14 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
>>>  	 */
>>>  	if (sync) {
>>>  		tg = task_group(current);
>>> -		weight = current->se.load.weight;
>>> +		weight = current->se.avg.load_avg_contrib;
>>>
>>>  		this_load += effective_load(tg, this_cpu, -weight, -weight);
>>>  		load += effective_load(tg, prev_cpu, 0, -weight);
>>>  	}
>>>
>>>  	tg = task_group(p);
>>> -	weight = p->se.load.weight;
>>> +	weight = p->se.avg.load_avg_contrib;
>>>
>>>  	/*
>>>  	 * In low-load situations, where prev_cpu is idle and this_cpu is idle
>>>
>>
> 

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