linux-kernel - Re: [PATCH 3/5] sched/deadline: Fix accounting after global limits change

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Message-ID: <aHYoYnnzqUlM1Bng@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 15 Jul 2025 12:07:30 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...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>,
	Waiman Long <llong@...hat.com>, linux-kernel@...r.kernel.org,
	Marcel Ziswiler <marcel.ziswiler@...ethink.co.uk>,
	Luca Abeni <luca.abeni@...tannapisa.it>
Subject: Re: [PATCH 3/5] sched/deadline: Fix accounting after global limits
 change

On 14/07/25 10:59, Peter Zijlstra wrote:
> On Fri, Jun 27, 2025 at 01:51:16PM +0200, Juri Lelli wrote:
> 
> > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> > index 15d5855c542cb..be6e9bcbe82b6 100644
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -2886,6 +2886,12 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
> >  	sched_domains_mutex_unlock();
> >  	mutex_unlock(&mutex);
> >  
> > +	/*
> > +	 * After changing maximum available bandwidth for DEADLINE, we need to
> > +	 * recompute per root domain and per cpus variables accordingly.
> > +	 */
> > +	rebuild_sched_domains();
> > +
> >  	return ret;
> >  }
> 
> So I'll merge these patches since correctness first etc. But the above

Thanks!

> is quite terrible. It would be really good not to have to rebuild the
> sched domains for every rt change. Surely we can iterate the existing
> domains and update stuff?

Yeah, I agree. Tried doing an update at first, but then the involved
locking and the not so pleasant thing I could come up with made me
decide for the big hammer. Also because it should be a very infrequent
operation anyway.

But, I will try again somewhat soon.

Thanks,
Juri