linux-kernel - Re: [PATCH 2/2] sched/rt: update limit of sched

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Message-ID: <Z8ld-hutVNH3_aXF@jlelli-thinkpadt14gen4.remote.csb>
Date: Thu, 6 Mar 2025 08:34:02 +0000
From: Juri Lelli <juri.lelli@...hat.com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, peterz@...radead.org,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, hbathini@...ux.ibm.com, joelagnelf@...dia.com
Subject: Re: [PATCH 2/2] sched/rt: update limit of sched_rt sysctl in
 documentation

Hi,

On 06/03/25 10:59, Shrikanth Hegde wrote:
> By default fair_server dl_server allocates 5% of the bandwidth to the root
> domain. Due to this writing any value less than 5% fails due to -EBUSY.
> 
> cat /proc/sys/kernel/sched_rt_period_us
> 1000000
> $ echo 49999 > /proc/sys/kernel/sched_rt_runtime_us
> -bash: echo: write error: Device or resource busy
> $ echo 50000 > /proc/sys/kernel/sched_rt_runtime_us
> $
> 
> Since the sched_rt_runtime_us allows -1 as the minimum, put this
> restriction in the documentation.
> 
> One should check average of runtime/period in 
> /sys/kernel/debug/sched/fair_server/cpuX/* for exact value.
> 
> Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
> ---
>  Documentation/scheduler/sched-rt-group.rst | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Documentation/scheduler/sched-rt-group.rst b/Documentation/scheduler/sched-rt-group.rst
> index 80b05a3009ea..ab464335d320 100644
> --- a/Documentation/scheduler/sched-rt-group.rst
> +++ b/Documentation/scheduler/sched-rt-group.rst
> @@ -102,6 +102,9 @@ The system wide settings are configured under the /proc virtual file system:
>    * sched_rt_period_us takes values from 1 to INT_MAX.
>    * sched_rt_runtime_us takes values from -1 to sched_rt_period_us.
>    * A run time of -1 specifies runtime == period, ie. no limit.
> +  * sched_rt_runtime_us/sched_rt_period_us > 0.05 inorder to preserve
> +    bandwidth for fair dl_server. For accurate value check average of
> +    runtime/period in /sys/kernel/debug/sched/fair_server/cpuX/

Looks good to me.

Reviewed-by: Juri Lelli <juri.lelli@...hat.com>

Thanks!
Juri