linux-kernel - Re: [PATCH 1/2] sched: Use do_div() for 64 bit division at power utilization calculation (putil)

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Date:	Thu, 30 May 2013 09:48:58 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Lukasz Majewski <l.majewski@...sung.com>
CC:	Linux PM list <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH 1/2] sched: Use do_div() for 64 bit division at power
 utilization calculation (putil)

On 05/23/2013 04:34 PM, Lukasz Majewski wrote:
> Now explicit casting is done when power usage variable (putil) is calculated
> 
> Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
> ---
> This patch was developed on top of the following Alex's repository:
> https://github.com/alexshi/power-scheduling/commits/power-scheduling
> ---
>  kernel/sched/fair.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 


Thanks for catch this issue. seems use div_u64 is better, and there are 2 same bugs.
so, could I rewrite the patch like following?
---

>From 9f72c25607351981898d99822f5a66e0ca67a3da Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@...el.com>
Date: Wed, 29 May 2013 11:09:39 +0800
Subject: [PATCH 1/2] sched: fix cast on power utilization calculation and use
 div_u64

Now explicit casting is done when power usage variable (putil) is
calculated.
div_u64 is optimized on u32.

Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
Signed-off-by: Alex Shi <alex.shi@...el.com>
---
 kernel/sched/fair.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 09ae48a..3a4917c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1504,8 +1504,8 @@ static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
 	__update_tg_runnable_avg(&rq->avg, &rq->cfs);
 
 	period = rq->avg.runnable_avg_period ? rq->avg.runnable_avg_period : 1;
-	rq->util = (u64)(rq->avg.runnable_avg_sum << SCHED_POWER_SHIFT)
-				/ period;
+	rq->util = div_u64(((u64)rq->avg.runnable_avg_sum << SCHED_POWER_SHIFT),
+				period);
 }
 
 /* Add the load generated by se into cfs_rq's child load-average */
@@ -3407,8 +3407,8 @@ static int is_sd_full(struct sched_domain *sd,
 		/* p maybe a new forked task */
 		putil = FULL_UTIL;
 	else
-		putil = (u64)(p->se.avg.runnable_avg_sum << SCHED_POWER_SHIFT)
-				/ (p->se.avg.runnable_avg_period + 1);
+		putil = div_u64(((u64)p->se.avg.runnable_avg_sum << SCHED_POWER_SHIFT),
+				p->se.avg.runnable_avg_period + 1);
 
 	/* Try to collect the domain's utilization */
 	group = sd->groups;
@@ -3463,9 +3463,11 @@ find_leader_cpu(struct sched_group *group, struct task_struct *p, int this_cpu,
 	int vacancy, min_vacancy = INT_MAX;
 	int leader_cpu = -1;
 	int i;
+
 	/* percentage of the task's util */
-	unsigned putil = (u64)(p->se.avg.runnable_avg_sum << SCHED_POWER_SHIFT)
-				/ (p->se.avg.runnable_avg_period + 1);
+	unsigned putil;
+	putil = div_u64(((u64)p->se.avg.runnable_avg_sum << SCHED_POWER_SHIFT),
+				p->se.avg.runnable_avg_period + 1);
 
 	/* bias toward local cpu */
 	if (cpumask_test_cpu(this_cpu, tsk_cpus_allowed(p)) &&
-- 
1.7.12


-- 
Thanks
    Alex
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