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

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Message-ID: <518749A9.8000605@linux.vnet.ibm.com>
Date:	Mon, 06 May 2013 14:11:53 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Alex Shi <alex.shi@...el.com>
CC:	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, preeti@...ux.vnet.ibm.com,
	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

On 05/06/2013 01:39 PM, Alex Shi wrote:
> On 05/06/2013 11:34 AM, Michael Wang wrote:
>>>> @@ -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?
> 
> 
> thanks for testing, Michael!
> 
> Maybe 2 fix worth to try.
> 
> 1, change back the tg_weight in calc_tg_weight() to use tg_load_contrib not direct load.
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 6f4f14b..c770f8d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1037,8 +1037,8 @@ static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
>  	 * update_cfs_rq_load_contribution().
>  	 */
>  	tg_weight = atomic64_read(&tg->load_avg);
> -	tg_weight -= cfs_rq->tg_load_contrib;
> -	tg_weight += cfs_rq->load.weight;
> +	//tg_weight -= cfs_rq->tg_load_contrib;
> +	//tg_weight += cfs_rq->load.weight;
> 
>  	return tg_weight;
>  }
> 
> 2, another try is follow the current calc_tg_weight, so remove the follow change.
> 
>>>> @@ -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;
> 
> Would you like to try them?

Sure, I will take a try on both :)

But actually I'm wondering whether it is necessary to change
effective_load()?

It is only severed for wake-affine and the whole stuff is still in the
dark, if patch 1~6 already show good results, why don't we leave it there?

So how about the situation on your box without the last patch? is the
benefit still there?

Regards,
Michael Wang

> 
> 

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