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

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Message-ID: <Z0c8S8i3qt7SEU14@jlelli-thinkpadt14gen4.remote.csb>
Date: Wed, 27 Nov 2024 16:35:39 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	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

Hi Michal,

On 27/11/24 11:55, Michal Koutný wrote:
> 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%?

Yes, it is indeed.

Best,
Juri