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

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Message-ID: <d3bllrfwji74t3ix3jcdlvdt6jdorw75wjol6kmadpeuuqal2t@io7ghgf7zkbs>
Date: Wed, 27 Nov 2024 11:55:43 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Daniel Bristot de Oliveira <bristot@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	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>, 
	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

Hello.

(I'm replying now as I installed v6.12 and this message has the
context.)

On Mon, May 27, 2024 at 02:06:55PM GMT, Daniel Bristot de Oliveira <bristot@...nel.org> wrote:
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 0dbb42cf7fe6..7df8179bfa08 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1554,6 +1554,7 @@ static void update_curr_dl_se(struct rq *rq, struct sched_dl_entity *dl_se, s64
>  	if (dl_se == &rq->fair_server)
>  		return;
>  
> +#ifdef CONFIG_RT_GROUP_SCHED
>  	/*
>  	 * Because -- for now -- we share the rt bandwidth, we need to
>  	 * account our runtime there too, otherwise actual rt tasks
> @@ -1578,6 +1579,7 @@ static void update_curr_dl_se(struct rq *rq, struct sched_dl_entity *dl_se, s64
>  			rt_rq->rt_time += delta_exec;
>  		raw_spin_unlock(&rt_rq->rt_runtime_lock);
>  	}
> +#endif
>  }
>  
>  /*
> @@ -1632,8 +1634,7 @@ void dl_server_start(struct sched_dl_entity *dl_se)
>  	 * this before getting generic.
>  	 */
>  	if (!dl_server(dl_se)) {
> -		/* Disabled */
> -		u64 runtime = 0;
> +		u64 runtime =  50 * NSEC_PER_MSEC;
>  		u64 period = 1000 * NSEC_PER_MSEC;
>  
>  		dl_server_apply_params(dl_se, runtime, period, 1);

The global_rt_runtime() also applies to deadline class when CPU's DL
bandwidth is init'd in init_dl_rq_bw_ratio().

The default DL bandwidth is thus is 95%. The fair server is given 5%.
Is that 5% of those 95%?

Or is it meant to be complementary? (Perhaps not as I can configure
rt_runtime_us/rt_period_us > 95% without an error. But then I don't
understand what the global rt_runtime_us (w/out CONFIG_RT_GROUP_SCHED)
configures.)

Thanks for some hints,
Michal


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