linux-kernel - Re: [PATCH] sched/deadline: Add DL server activated message

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Message-ID: <aJSo1bvZ54Kl_vKb@jlelli-thinkpadt14gen4.remote.csb>
Date: Thu, 7 Aug 2025 14:23:33 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: Kuyo Chang <kuyo.chang@...iatek.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>,
	Valentin Schneider <vschneid@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] sched/deadline: Add DL server activated message

On 07/08/25 15:52, Kuyo Chang wrote:
> On Thu, 2025-08-07 at 08:15 +0100, Juri Lelli wrote:
> > 
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> > 
> > 
> > Hi,
> > 
> > On 05/08/25 23:53, Kuyo Chang wrote:
> > > From: kuyo chang <kuyo.chang@...iatek.com>
> > > 
> > > The DL server is introduced as a replacement for realtime
> > > throttling.
> > > When RT throttling is activated, a message
> > > "sched: RT throttling activated" is shown. However, it is currently
> > > difficult for users to know when the DL server is activated.
> > > 
> > > This patch adds a similar message to indicate when the DL server
> > > is activated, which helps users debug RT/CFS contention issues.
> > > 
> > > Signed-off-by: kuyo chang <kuyo.chang@...iatek.com>
> > > ---
> > >  kernel/sched/deadline.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > > index e2d51f4306b3..8e0de6cdb980 100644
> > > --- a/kernel/sched/deadline.c
> > > +++ b/kernel/sched/deadline.c
> > > @@ -2042,6 +2042,9 @@ enqueue_dl_entity(struct sched_dl_entity
> > > *dl_se, int flags)
> > >       }
> > > 
> > >       __enqueue_dl_entity(dl_se);
> > > +
> > > +     if (dl_server(dl_se))
> > > +             printk_deferred_once("sched: dl_server activated\n");
> > >  }
> > 
> > Not sure if we want/need this, but, if we do, I believe
> > fair_server_pick_task() might be a better place to put it, as it's
> > really when the dl-server is called to do its job.
> > 
> 
> Thanks for your suggestion, maybe the minor patch as below
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index e2d51f4306b3..82d1091e56f5 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2395,6 +2395,7 @@ static struct task_struct *__pick_task_dl(struct
> rq *rq)
>  			goto again;
>  		}
>  		rq->dl_server = dl_se;
> +		printk_deferred_once("sched: dl_server activated\n");

Guess it could work. If we are going to add this, maybe printing
information about the task dl-server is servicing might also be
interesting.