linux-kernel - Re: [PATCH v2] sched/deadline: Reset dl

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Message-ID: <b7ffc7e6121320d29cedcff0e2b68ad76c8e2775.camel@redhat.com>
Date: Thu, 29 Jan 2026 12:48:35 +0100
From: gmonaco@...hat.com
To: Andrea Righi <arighi@...dia.com>
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>, Valentin Schneider	 <vschneid@...hat.com>, Tejun
 Heo <tj@...nel.org>, Joel Fernandes	 <joelagnelf@...dia.com>, David Vernet
 <void@...ifault.com>, Changwoo Min	 <changwoo@...lia.com>, Daniel Hodges
 <hodgesd@...a.com>, 	sched-ext@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/deadline: Reset dl_server execution state on
 stop

On Wed, 2026-01-28 at 14:41 +0100, Andrea Righi wrote:
> Just to make sure we're testing the same thing, I'm currently using
> https://git.kernel.org/pub/scm/linux/kernel/git/arighi/linux.git,
> branch
> scx-dl-server.
> 
> I'm running this test inside virtme-ng:
>   $ vng -vb --config tools/testing/selftests/sched_ext/config
>   $ vng -v -- tools/testing/selftests/sched_ext/runner -t rt_stall

Well, that's a fun one, I could reproduce the same failure you
described in vng on another x86 box.

The arm box (bare metal) I used initially still passes just fine all 4
iterations of the test.

On the x86 box (vng) I tried different orders of iterations (where the
original is fair-ext-fair-ext) with and without the ext server active.

No ext-server: the ext iteration fails and breaks also fair (unlike the
arm64 box where the fair was intact)
ext-server active: a sequence fair-ext breaks both (like you observe).

I don't have time to look further into this right now, but it looks
like an interesting pattern.

Thanks,
Gabriele