Received-SPF: pass (google.com: domain of linux-kernel+bounces-62885-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Message-ID: <cced2edb-b4ac-4035-9930-9e41eeb1f263@joelfernandes.org>
Date: Mon, 12 Feb 2024 21:21:10 -0500
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v5 7/7] sched/fair: Fair server interface
Content-Language: en-US
From: Joel Fernandes <joel@joelfernandes.org>
To: Daniel Bristot de Oliveira <bristot@kernel.org>,
 Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
 Juri Lelli <juri.lelli@redhat.com>,
 Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
 Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>,
 Mel Gorman <mgorman@suse.de>, Daniel Bristot de Oliveira
 <bristot@redhat.com>, Valentin Schneider <vschneid@redhat.com>,
 linux-kernel@vger.kernel.org, Luca Abeni <luca.abeni@santannapisa.it>,
 Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
 Thomas Gleixner <tglx@linutronix.de>,
 Vineeth Pillai <vineeth@bitbyteword.org>,
 Shuah Khan <skhan@linuxfoundation.org>, Phil Auld <pauld@redhat.com>,
 Suleiman Souhlal <suleiman@google.com>, youssefesmat@google.com
References: <cover.1699095159.git.bristot@kernel.org>
 <26adad2378c8b15533e4f6216c2863341e587f57.1699095159.git.bristot@kernel.org>
 <8cbf4bcd-431b-466f-b62d-ee03932e97f5@joelfernandes.org>
In-Reply-To: <8cbf4bcd-431b-466f-b62d-ee03932e97f5@joelfernandes.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit


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