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

From: Daniel Bristot de Oliveira <bristot@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	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>,
	Joel Fernandes <joel@joelfernandes.org>,
	Vineeth Pillai <vineeth@bitbyteword.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Phil Auld <pauld@redhat.com>
Subject: Re: [PATCH v5 7/7] sched/fair: Fair server interface
Date: Mon, 6 Nov 2023 17:29:49 +0100	[thread overview]
Message-ID: <9a7222ed-88f8-4a3f-9d83-09b7fb977c27@kernel.org> (raw)
In-Reply-To: <20231106154042.GH3818@noisy.programming.kicks-ass.net>

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?