linux-kernel - Re: [patch v7 7/8] sched: consider runnable load average in move

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Date:	Fri, 31 May 2013 23:07:37 +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>,
	"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>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mgorman@...e.de" <mgorman@...e.de>,
	"riel@...hat.com" <riel@...hat.com>,
	"wangyun@...ux.vnet.ibm.com" <wangyun@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>,
	Changlong Xie <changlongx.xie@...el.com>
Subject: Re: [patch v7 7/8] sched: consider runnable load average in move_tasks


> 
> runnable_load_avg is u64, so you need to use div_u64() similar to how it
> is already done in task_h_load() further down in this patch. It doesn't
> build on ARM as is.
> 
> Fix:
> -               load /= tg->parent->cfs_rq[cpu]->runnable_load_avg + 1;
> +               load = div_u64(load,
> 				tg->parent->cfs_rq[cpu]->runnable_load_avg + 1);
> 
> Morten

Thank a lot for review!

div_u64 or do_div will do force cast u32 on the divisor, so in 64bit machine, 
the divisor may become incorrect.
Since cfs_rq->runnable_load_avg is always smaller the cfs_rq.load.weight. and 
load.weight is 'unsigned long', we can cast the runnable_load_avg to 
'unsigned long' too. Than the div will fit on both 64/32 bit machine and no 
data concatenate!

So the patch changed as following.

BTW, Paul & Peter:
in cfs_rq, runnable_load_avg, blocked_load_avg, tg_load_contrib are all
u64, but their are similar with 'unsigned long' load.weight. So could we change
them to 'unsigned long'?

---

>From 4a17564363f6d65c9d513ad206b54ebd032d3f46 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@...el.com>
Date: Mon, 3 Dec 2012 23:00:53 +0800
Subject: [PATCH 7/8] sched: consider runnable load average in move_tasks

Except using runnable load average in background, move_tasks is also
the key functions in load balance. We need consider the runnable load
average in it in order to the apple to apple load comparison.

Morten catch a div u64 bug on ARM, thanks!

Signed-off-by: Alex Shi <alex.shi@...el.com>
---
 kernel/sched/fair.c |   17 ++++++++++-------
 1 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index eadd2e7..73e4507 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4178,11 +4178,14 @@ static int tg_load_down(struct task_group *tg, void *data)
 	long cpu = (long)data;
 
 	if (!tg->parent) {
-		load = cpu_rq(cpu)->load.weight;
+		load = cpu_rq(cpu)->avg.load_avg_contrib;
 	} else {
+		unsigned long tmp_rla;
+		tmp_rla = tg->parent->cfs_rq[cpu]->runnable_load_avg + 1;
+
 		load = tg->parent->cfs_rq[cpu]->h_load;
-		load *= tg->se[cpu]->load.weight;
-		load /= tg->parent->cfs_rq[cpu]->load.weight + 1;
+		load *= tg->se[cpu]->avg.load_avg_contrib;
+		load /= tmp_rla;
 	}
 
 	tg->cfs_rq[cpu]->h_load = load;
@@ -4208,12 +4211,12 @@ static void update_h_load(long cpu)
 static unsigned long task_h_load(struct task_struct *p)
 {
 	struct cfs_rq *cfs_rq = task_cfs_rq(p);
-	unsigned long load;
+	unsigned long load, tmp_rla;
 
-	load = p->se.load.weight;
-	load = div_u64(load * cfs_rq->h_load, cfs_rq->load.weight + 1);
+	load = p->se.avg.load_avg_contrib * cfs_rq->h_load;
+	tmp_rla = cfs_rq->runnable_load_avg + 1;
 
-	return load;
+	return load / tmp_rla;
 }
 #else
 static inline void update_blocked_averages(int cpu)
-- 
1.7.5.4

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