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

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Date:   Mon, 6 Nov 2023 17:29:49 +0100
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        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>,
        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>
Subject: Re: [PATCH v5 7/7] sched/fair: Fair server interface

On 11/6/23 16:40, Peter Zijlstra wrote:
> On Sat, Nov 04, 2023 at 11:59:24AM +0100, 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
>>
> 
> This then leaves /proc/sys/kernel/sched_rt_{period,runtime}_us to be the
> total available bandwidth control, right?

right, but thinking aloud... given that the per-cpu files are already allocating the
bandwidth on the dl_rq, the spare time for fair scheduler is granted.

Still, we can have them there as a safeguard to not overloading the deadline
scheduler... (thinking aloud 2) as long as global is a thing... as we get away
from it, that global limitation will make less sense - still better to have a form
of limitation so people are aware of bandwidth until there.

> But then shouldn've we also rip out the throttle thingy right quick?
> 

I was thinking about moving the entire throttling machinery inside CONFIG_RT_GROUP_SCHED
for now, because GROUP_SCHED depends on it, no?

With the next step on moving the dl server as the base for the hierarchical scheduling...
That will rip out the CONFIG_RT_GROUP_SCHED... with a thing with a per-cpu interface.

Does it make sense?