linux-kernel - Re: [PATCH 03/10] sched: Clean-up struct sd_lb

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Date:	Mon, 26 Aug 2013 10:56:39 +0800
From:	Lei Wen <adrian.wenl@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	linux-kernel@...r.kernel.org, Mike Galbraith <efault@....de>,
	Paul Turner <pjt@...gle.com>, Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Lei Wen <leiwen@...vell.com>, Rik van Riel <riel@...riel.com>,
	Joonsoo Kim <js1304@...il.com>
Subject: Re: [PATCH 03/10] sched: Clean-up struct sd_lb_stat

On Tue, Aug 20, 2013 at 12:01 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> There is no reason to maintain separate variables for this_group
> and busiest_group in sd_lb_stat, except saving some space.
> But this structure is always allocated in stack, so this saving
> isn't really benificial [peterz: reducing stack space is good; in this
> case readability increases enough that I think its still beneficial]
>
> This patch unify these variables, so IMO, readability may be improved.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> [peterz: lots of style edits, a few fixes and a rename]
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Link: http://lkml.kernel.org/r/1375778203-31343-4-git-send-email-iamjoonsoo.kim@lge.com
> ---
>  kernel/sched/fair.c |  225 +++++++++++++++++++++++++---------------------------
>  1 file changed, 112 insertions(+), 113 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4277,36 +4277,6 @@ static unsigned long task_h_load(struct
>
[snip]...
> -       env->imbalance = DIV_ROUND_CLOSEST(
> -               sds->max_load * sds->busiest->sgp->power, SCHED_POWER_SCALE);
> +       env->imbalance = DIV_ROUND_CLOSEST(sds->busiest_stat.avg_load *
> +                               sds->busiest->sgp->power, SCHED_POWER_SCALE);
>

I am wondering whether we could change this line as below is more appropriate,
since it would avoid the division here:
       env->imbalance = (sds->busiest_stat.avg_load * sds->busiest->sgp->power)
                                      >> SCHED_POWER_SHIFT;

I am not sure whether compiler would be smarter enough to covert into
>> operation,
if it see SCHED_POWER_SCALE is 1024 here.

Thanks,
Lei
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