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

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Date:	Mon, 06 May 2013 12:40:07 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Michael Wang <wangyun@...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 Alex,Michael,

Can you try out the below patch and check? 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.

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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