linux-kernel - Re: [PATCH V7 9/9] sched/rt: Remove default bandwidth control

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Message-ID: <tjsas6vkv3xegcgmranxmnkrt46xuitp553caz6vvtgpfrbwl3@252nbydvxaqt>
Date: Fri, 29 Nov 2024 11:02:36 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Juri Lelli <juri.lelli@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>, 
	linux-kernel@...r.kernel.org, Luca Abeni <luca.abeni@...tannapisa.it>, 
	Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>, Thomas Gleixner <tglx@...utronix.de>, 
	Joel Fernandes <joel@...lfernandes.org>, Vineeth Pillai <vineeth@...byteword.org>, 
	Shuah Khan <skhan@...uxfoundation.org>, Phil Auld <pauld@...hat.com>, 
	Suleiman Souhlal <suleiman@...gle.com>, Youssef Esmat <youssefesmat@...gle.com>
Subject: Re: [PATCH V7 9/9] sched/rt: Remove default bandwidth control

On Wed, Nov 27, 2024 at 04:35:39PM GMT, Juri Lelli <juri.lelli@...hat.com> wrote:
> > The default DL bandwidth is thus is 95%. The fair server is given 5%.
> > Is that 5% of those 95%?
> 
> Yes, it is indeed.

Thanks for navigating me. I have followup questions about
/proc/sys/kernel/sched_rt_runtime_us / /proc/sys/kernel/sched_rt_period_us
(a ratio, without CONGIG_RT_GROUP_SCHED)

- 0
  - disables DL, (not RT, so they can monopolize a CPU)
- 1
  - DL tasks can monopolize CPU, SCHED_NORMAL have 5% thanks to
    fair_server
- 1-Δ
  - SCHED_NORMAL tasks have
    - (1-Δ)*5% on behalf of DL (above RT)
    - Δ regularly (below RT)

Is this breakdown correct?
I'm wondering if different values of Δ mean anything or how they can be
used.

Regards,
Michal

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