linux-kernel - Re: [PATCH 4/7] sched_ext: Add a DL server for sched

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Message-ID: <aXEMat4IoNnGYgxw@gpd4>
Date: Wed, 21 Jan 2026 18:27:06 +0100
From: Andrea Righi <arighi@...dia.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, 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>,
	Valentin Schneider <vschneid@...hat.com>,
	Joel Fernandes <joelagnelf@...dia.com>, Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Shuah Khan <shuah@...nel.org>,
	sched-ext@...ts.linux.dev, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Christian Loehle <christian.loehle@....com>
Subject: Re: [PATCH 4/7] sched_ext: Add a DL server for sched_ext tasks

On Wed, Jan 21, 2026 at 04:52:45PM +0100, Peter Zijlstra wrote:
> On Wed, Jan 21, 2026 at 01:49:38PM +0100, Andrea Righi wrote:
> > On Wed, Jan 21, 2026 at 01:29:01PM +0100, Peter Zijlstra wrote:
> > > On Tue, Jan 20, 2026 at 10:50:35PM +0100, Andrea Righi wrote:
> > > 
> > > > @@ -1813,6 +1813,7 @@ void dl_server_stop(struct sched_dl_entity *dl_se)
> > > >  	hrtimer_try_to_cancel(&dl_se->dl_timer);
> > > >  	dl_se->dl_defer_armed = 0;
> > > >  	dl_se->dl_throttled = 0;
> > > > +	dl_se->dl_defer_running = 0;
> > > >  	dl_se->dl_defer_idle = 0;
> > > >  	dl_se->dl_server_active = 0;
> > > >  }
> > > 
> > > This should definitely not be in this patch. Why was this added? Were
> > > you trying to do the same as:
> > > 
> > >   ca1e8eede4fc ("sched/deadline: Fix server stopping with runnable tasks")
> > > 
> > 
> > The problem is that if remove this, RT can completely stall EXT tasks, also
> > with ca1e8eede4fc applied.
> 
> But that's not something ext specific, right? Can you pull this change
> out and write a sane Changelog for it, describing the problem and so?

Yeah, this should happen with fair as well. I'll try to reproduce the
problem without ext and try to get more info.

Thanks,
-Andrea