linux-kernel - Re: [PATCH v5 7/7] sched/fair: Fair server interface

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Date: Mon, 12 Feb 2024 21:21:10 -0500
From: Joel Fernandes <joel@...lfernandes.org>
To: Daniel Bristot de Oliveira <bristot@...nel.org>,
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>
Cc: 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>,
 Vineeth Pillai <vineeth@...byteword.org>,
 Shuah Khan <skhan@...uxfoundation.org>, Phil Auld <pauld@...hat.com>,
 Suleiman Souhlal <suleiman@...gle.com>, youssefesmat@...gle.com
Subject: Re: [PATCH v5 7/7] sched/fair: Fair server interface



On 2/12/2024 9:13 PM, Joel Fernandes wrote:
> 
> 
> On 11/4/2023 6:59 AM, Daniel Bristot de Oliveira wrote:
>> Add an interface for fair server setup on debugfs.
>>
>> Each rq have three files under /sys/kernel/debug/sched/rq/CPU{ID}:
>>
>>  - fair_server_runtime: set runtime in ns
>>  - fair_server_period: set period in ns
>>  - fair_server_defer: on/off for the defer mechanism
> 
> Btw Daniel, there is an interesting side-effect of this interface having runtime
> and period in 2 separate files :)
> 
> Say I want to set a CPU to 5ms / 10ms.
> 

Sorry let me try again, say I want to set 500us / 1ms.

Then I have to do the following to get it to work:

# echo 100000000 > /sys/kernel/debug/sched/fair_server/cpu0/period
# echo 5000000 > /sys/kernel/debug/sched/fair_server/cpu0/runtime
# echo 10000000 > /sys/kernel/debug/sched/fair_server/cpu0/period
# echo 500000 > /sys/kernel/debug/sched/fair_server/cpu0/runtime
# echo 1000000 > /sys/kernel/debug/sched/fair_server/cpu0/period

IOW, if I boot and do the following, it fails:

# echo 500000 > /sys/kernel/debug/sched/fair_server/cpu0/runtime
bash: echo: write error: Device or resource busy

 - Joel