linux-kernel - Re: [RFC patch 1/4] sched: change cfs

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Message-ID: <CAKfTPtA=pVQ69pfv97kgcdawgHbQbkbXW4sFGN6_bAzZcD9b9Q@mail.gmail.com>
Date:	Fri, 7 Jun 2013 11:07:28 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, Paul Turner <pjt@...gle.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, riel@...hat.com,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>
Subject: Re: [RFC patch 1/4] sched: change cfs_rq load avg to unsigned long

On 7 June 2013 09:29, Alex Shi <alex.shi@...el.com> wrote:
> Since the 'u64 runnable_load_avg, blocked_load_avg' in cfs_rq struct are
> smaller than 'unsigned long' cfs_rq->load.weight. We don't need u64
> vaiables to describe them. unsigned long is more efficient and convenience.
>

Hi Alex,

I just want to point out that we can't have more than 48388 tasks with
highest priority on a runqueue with an unsigned long on a 32 bits
system.  I don't know if we can reach such kind of limit on a 32bits
machine ? For sure, not on an embedded system.

Regards,
Vincent

> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  kernel/sched/debug.c | 4 ++--
>  kernel/sched/sched.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 75024a6..160afdc 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -211,9 +211,9 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
>         SEQ_printf(m, "  .%-30s: %ld\n", "load", cfs_rq->load.weight);
>  #ifdef CONFIG_FAIR_GROUP_SCHED
>  #ifdef CONFIG_SMP
> -       SEQ_printf(m, "  .%-30s: %lld\n", "runnable_load_avg",
> +       SEQ_printf(m, "  .%-30s: %ld\n", "runnable_load_avg",
>                         cfs_rq->runnable_load_avg);
> -       SEQ_printf(m, "  .%-30s: %lld\n", "blocked_load_avg",
> +       SEQ_printf(m, "  .%-30s: %ld\n", "blocked_load_avg",
>                         cfs_rq->blocked_load_avg);
>         SEQ_printf(m, "  .%-30s: %lld\n", "tg_load_avg",
>                         (unsigned long long)atomic64_read(&cfs_rq->tg->load_avg));
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 8bc66c6..5a80943 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -277,7 +277,7 @@ struct cfs_rq {
>          * This allows for the description of both thread and group usage (in
>          * the FAIR_GROUP_SCHED case).
>          */
> -       u64 runnable_load_avg, blocked_load_avg;
> +       unsigned long runnable_load_avg, blocked_load_avg;
>         atomic64_t decay_counter, removed_load;
>         u64 last_decay;
>
> --
> 1.7.12
>
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