linux-kernel - Re: [PATCH] sched/rt: Redefine RR

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Message-ID: <d5753b42-4422-a9a3-b35b-43b267797a61@linux.dev>
Date:   Wed, 8 Nov 2023 19:02:14 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/rt: Redefine RR_TIMESLICE to 100 msecs


Kindly ping...

Thanks


On 2023/10/18 16:17, Yajun Deng wrote:
> The RR_TIMESLICE is currently defined as the jiffies corresponding to
> 100 msecs. And then sysctl_sched_rr_timeslice will convert RR_TIMESLICE
> to 100 msecs. These are opposite calculations.
>
> There are msecs_to_jiffies and jiffies_to_msecs in sched_rr_handler.
> These are also opposite calculations.
>
> Redefine RR_TIMESLICE to 100 msecs, only sched_rr_timeslice needs to
> convert RR_TIMESLICE to jiffies.
>
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
>   include/linux/sched/rt.h |  2 +-
>   init/init_task.c         |  2 +-
>   kernel/sched/rt.c        | 12 +++++-------
>   3 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/sched/rt.h b/include/linux/sched/rt.h
> index b2b9e6eb9683..74f8f456a804 100644
> --- a/include/linux/sched/rt.h
> +++ b/include/linux/sched/rt.h
> @@ -58,6 +58,6 @@ extern void normalize_rt_tasks(void);
>    * default timeslice is 100 msecs (used only for SCHED_RR tasks).
>    * Timeslices get refilled after they expire.
>    */
> -#define RR_TIMESLICE		(100 * HZ / 1000)
> +#define RR_TIMESLICE		(100)
>   
>   #endif /* _LINUX_SCHED_RT_H */
> diff --git a/init/init_task.c b/init/init_task.c
> index 5727d42149c3..86619a425342 100644
> --- a/init/init_task.c
> +++ b/init/init_task.c
> @@ -94,7 +94,7 @@ struct task_struct init_task
>   	},
>   	.rt		= {
>   		.run_list	= LIST_HEAD_INIT(init_task.rt.run_list),
> -		.time_slice	= RR_TIMESLICE,
> +		.time_slice	= (RR_TIMESLICE * HZ) / MSEC_PER_SEC,
>   	},
>   	.tasks		= LIST_HEAD_INIT(init_task.tasks),
>   #ifdef CONFIG_SMP
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 6aaf0a3d6081..7c0e912094a9 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -4,7 +4,7 @@
>    * policies)
>    */
>   
> -int sched_rr_timeslice = RR_TIMESLICE;
> +int sched_rr_timeslice = (RR_TIMESLICE * HZ) / MSEC_PER_SEC;
>   /* More than 4 hours if BW_SHIFT equals 20. */
>   static const u64 max_rt_runtime = MAX_BW;
>   
> @@ -25,7 +25,7 @@ int sysctl_sched_rt_period = 1000000;
>   int sysctl_sched_rt_runtime = 950000;
>   
>   #ifdef CONFIG_SYSCTL
> -static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
> +static int sysctl_sched_rr_timeslice = RR_TIMESLICE;
>   static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
>   		size_t *lenp, loff_t *ppos);
>   static int sched_rr_handler(struct ctl_table *table, int write, void *buffer,
> @@ -3014,12 +3014,10 @@ static int sched_rr_handler(struct ctl_table *table, int write, void *buffer,
>   	 * Also, writing zero resets the timeslice to default:
>   	 */
>   	if (!ret && write) {
> -		sched_rr_timeslice =
> -			sysctl_sched_rr_timeslice <= 0 ? RR_TIMESLICE :
> -			msecs_to_jiffies(sysctl_sched_rr_timeslice);
> -
>   		if (sysctl_sched_rr_timeslice <= 0)
> -			sysctl_sched_rr_timeslice = jiffies_to_msecs(RR_TIMESLICE);
> +			sysctl_sched_rr_timeslice = RR_TIMESLICE;
> +
> +		sched_rr_timeslice = msecs_to_jiffies(sysctl_sched_rr_timeslice);
>   	}
>   	mutex_unlock(&mutex);
>