linux-kernel - Re: [PATCH v2 1/2] sched/fair: Fix how load gets propagated from cfs_rq to its sched

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Date:   Thu, 4 May 2017 12:26:57 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
        Chris Mason <clm@...com>, kernel-team@...com
Subject: Re: [PATCH v2 1/2] sched/fair: Fix how load gets propagated from
 cfs_rq to its sched_entity

Le Wednesday 03 May 2017 à 20:00:28 (+0200), Peter Zijlstra a écrit :
> 
 
[snip]

> 
> Just FUDGE2 on its own seems to be the best on my system and is a change
> that makes sense (and something Paul recently pointed out as well).
> 
> The implementation isn't particularly pretty or fast, but should
> illustrate the idea.
> 
> Poking at the whole update_tg_cfs_load() thing only makes it worse after
> that. And while I agree that that code is mind bending; it seems to work
> OK-ish.
> 
> Tejun, Vincent, could you guys have a poke?

I have added below patch on to of your:
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3191,7 +3191,7 @@ update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se)
 			}
 		}
 	} else {
-		load = calc_cfs_shares(gcfs_rq, prop_type);
+		load = scale_load_down(calc_cfs_shares(gcfs_rq, prop_type));
 	}
 
 	delta = load - se->avg.load_avg;
-- 

The results for each configurations are :

** Config 1**
linaro@...aro-developer:~/schbench$cat /sys/module/fair/parameters/prop_type
1
linaro@...aro-developer:~/schbench$ sudo cat /sys/kernel/debug/sched_features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU RT_PUSH_IPI NO_FORCE_SD_OVERLAP RT_RUNTIME_SHARE NO_LB_MIN ATTACH_AGE_LOAD NO_FUDGE NO_FUDGE2 

Latency percentiles (usec)
	50.0000th: 252
	75.0000th: 346
	90.0000th: 438
	95.0000th: 485
	*99.0000th: 537
	99.5000th: 581
	99.9000th: 5768
	min=0, max=14202

** Config 2 **
linaro@...aro-developer:~/schbench$ cat /sys/module/fair/parameters/prop_type
1
linaro@...aro-developer:~/schbench$ sudo cat /sys/kernel/debug/sched_features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU RT_PUSH_IPI NO_FORCE_SD_OVERLAP RT_RUNTIME_SHARE NO_LB_MIN ATTACH_AGE_LOAD FUDGE NO_FUDGE2 

Latency percentiles (usec)
	50.0000th: 261
	75.0000th: 374
	90.0000th: 457
	95.0000th: 490
	*99.0000th: 533
	99.5000th: 585
	99.9000th: 9392
	min=0, max=13295

**Config 3**
linaro@...aro-developer:~/schbench$ cat /sys/module/fair/parameters/prop_type
1
linaro@...aro-developer:~/schbench$ sudo cat /sys/kernel/debug/sched_features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU RT_PUSH_IPI NO_FORCE_SD_OVERLAP RT_RUNTIME_SHARE NO_LB_MIN ATTACH_AGE_LOAD NO_FUDGE FUDGE2 

Latency percentiles (usec)
	50.0000th: 233
	75.0000th: 309
	90.0000th: 456
	95.0000th: 498
	*99.0000th: 5272
	99.5000th: 8184
	99.9000th: 12368
	min=0, max=14865

I have run several time the test, few were correct but most of them were like
above

**Config 4**
linaro@...aro-developer:~/schbench$ cat /sys/module/fair/parameters/prop_type
1
linaro@...aro-developer:~/schbench$ sudo cat /sys/kernel/debug/sched_features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU RT_PUSH_IPI NO_FORCE_SD_OVERLAP RT_RUNTIME_SHARE NO_LB_MIN ATTACH_AGE_LOAD FUDGE FUDGE2 

Latency percentiles (usec)
	50.0000th: 211
	75.0000th: 290
	90.0000th: 380
	95.0000th: 451
	*99.0000th: 1778
	99.5000th: 5048
	99.9000th: 12752
	min=0, max=15090

I have run several time the test, few were correct but most of them were like
above

** Config 5 **
linaro@...aro-developer:~/schbench$ cat /sys/module/fair/parameters/prop_type
0
linaro@...aro-developer:~/schbench$ sudo cat /sys/kernel/debug/sched_features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU RT_PUSH_IPI NO_FORCE_SD_OVERLAP RT_RUNTIME_SHARE NO_LB_MIN ATTACH_AGE_LOAD FUDGE FUDGE2

Latency percentiles (usec)
	50.0000th: 216
	75.0000th: 297
	90.0000th: 430
	95.0000th: 487
	*99.0000th: 2748
	99.5000th: 7432
	99.9000th: 12912
	min=0, max=15046

I have run several time the test, few were correct but most of them were like
above

** Config 6 **
linaro@...aro-developer:~/schbench$ cat /sys/module/fair/parameters/prop_type
0
linaro@...aro-developer:~/schbench$ sudo cat /sys/kernel/debug/sched_features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_CAPACITY TTWU_QUEUE NO_SIS_AVG_CPU RT_PUSH_IPI NO_FORCE_SD_OVERLAP RT_RUNTIME_SHARE NO_LB_MIN ATTACH_AGE_LOAD FUDGE NO_FUDGE2 

Latency percentiles (usec)
	50.0000th: 245
	75.0000th: 339
	90.0000th: 444
	95.0000th: 492
	*99.0000th: 3036
	99.5000th: 9104
	99.9000th: 12496
	min=0, max=14098

I have run several time the test, few were correct but most of them were like
above



Config 1 and 2 are the two configuraton which have stable and good results

Regards,
Vincent