From: Mike Galbraith <efault@gmx.de>
To: Lukas Beckmann <lbckmnn@mailbox.org>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Sasha Levin <sashal@kernel.org>
Cc: regressions@lists.linux.dev, stable@vger.kernel.org,
linux-rt-users@vger.kernel.org
Subject: Re: [REGRESSION] 6.12.y: d66792919d4f (sched/deadline: Use revised wakeup rule for dl_server) causes latencies up to 50ms with PREEMPT_RT
Date: Mon, 11 May 2026 07:50:10 +0200 [thread overview]
Message-ID: <c3120aeed5b0bc34e96e39a9494986aa0fedd332.camel@gmx.de> (raw)
In-Reply-To: <04657838-46d1-432d-95e1-eb73b930b032@mailbox.org>
On Sun, 2026-05-10 at 22:57 +0200, Lukas Beckmann wrote:
> Hi,
Greetings!
> I am reporting a regression which was introduced by d66792919d4f on 6.12.y.
> Since this commit, cyclictest reports latencies up to 50 milliseconds,
> on kernels with CONFIG_PREEMPT_RT=y.
>
> Steps to reproduce:
> 1. run a load (e.g. stress-ng --cpu 4 --io 2 --vm 2 --vm-bytes 128M)
> 2. run cyclictest (e.g. cyclictest -a -t -m -p 80 -i 250 -d 0)
...
> I found this, because Debian updated its rt kernel from 6.12.74 to 6.12.85.
> The issue was also present with upstream 6.12.85 and HEAD, but not with
> 6.12.74, so I started bisecting and eventually found d66792919d4f.
>
> Is it possible to revert the commit?
>
> I can provide traces or help wth testing if needed.
FWIW, my box says this *may* be due to a fix (+follow-ups) that didn't
wander back to stable.
cccb45d7c429 ("sched/deadline: Less agressive dl_server handling")
Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server")
Follow-ups:
4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck")
a3a70caf7906 ("sched/deadline: Fix dl_server behaviour")
Local 6.12-rt tree containing the above (et al) failed to reproduce in
the hour I let it try to, whereas a build excluding only all locally
added fix backports reproduced in fairly short order.
Suspects NOT confirmed in total isolation...
-Mike
next prev parent reply other threads:[~2026-05-11 5:50 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-10 20:57 [REGRESSION] 6.12.y: d66792919d4f (sched/deadline: Use revised wakeup rule for dl_server) causes latencies up to 50ms with PREEMPT_RT Lukas Beckmann
2026-05-11 5:50 ` Mike Galbraith [this message]
2026-05-11 14:21 ` Sasha Levin
2026-05-11 15:30 ` Mike Galbraith
2026-05-11 22:08 ` Lukas Beckmann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c3120aeed5b0bc34e96e39a9494986aa0fedd332.camel@gmx.de \
--to=efault@gmx.de \
--cc=juri.lelli@redhat.com \
--cc=lbckmnn@mailbox.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=regressions@lists.linux.dev \
--cc=sashal@kernel.org \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox