From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-101.mailbox.org (mout-p-101.mailbox.org [80.241.56.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 460813043CE; Sun, 10 May 2026 20:57:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.151 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778446676; cv=none; b=kxPLkdGVvvZBAoUzSekw4hVuDD57U0sDcyLC5AYpREUQu7E2LHj1lOHNAmMEXA3cbAl/Thg4mwmN4nWmuwoHxt9ivJJTzDCJEDl90wlK0Bh8uKid+w71KTtT7EUm8UN/Ge1JJuyt06cC78jMqjoyDCfA62g2VanO6n45OqjFvn4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778446676; c=relaxed/simple; bh=U3XG11g75IcTjdRGvwT9tM9l7i7M8yifd56uOB36Wsk=; h=Message-ID:Date:MIME-Version:To:Cc:From:Subject:Content-Type; b=uKBPkhlFLyGFoi4F8LH+NTUgPsMuh1TMjxo8mOuGRQ46izWQ2Ie7aPRqMAXgxsKL2OgBpQ107WbADin7blRvmoXEIAqsmy0sCfWBONskdcM8Ggd4VGQXuMYIby02XsDxfjB4S1nMI4cZNpGnjqJhftCQCkvDOATTbxlN03Fmob8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org; spf=pass smtp.mailfrom=mailbox.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b=ZzEosxeQ; arc=none smtp.client-ip=80.241.56.151 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mailbox.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b="ZzEosxeQ" Received: from smtp2.mailbox.org (smtp2.mailbox.org [10.196.197.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-101.mailbox.org (Postfix) with ESMTPS id 4gDFYT6Sztz9t8W; Sun, 10 May 2026 22:57:49 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1778446670; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=JhbkDIgXOs/Y9f4bIfEtVjnIvM/A/84iZ7rQjx1TFrs=; b=ZzEosxeQ3kh0XSwlKI+79DS079iUxOiXPGpsqiiu79VPMcXIjnn26+3ubtGlQCgjHJsxkk EagOTRR+b9+YR6JzYKeh3yrsgHRPvCKwOyzmgvekp+og5URxGpm0gEKy+qE5VmF97gYUnF r8QkOgPbhElyJAF+XF0+cbNdv5g7ykd1ps+ahQsaV2zt2OPVd7pAhjEyQq22UAmynCTG1s 1p1LMZVj++ljAKqkP63C8yDP5YJUiiO575O7AFrB3cVuW/OdPTIR5PGwiIioVPj2Y36KmJ xW06mZmYzxRZG5WcxFocCOSECYNPKksU4u0RDRmN7ZUtZEuXWeRi6ZYpv5jN6Q== Message-ID: <04657838-46d1-432d-95e1-eb73b930b032@mailbox.org> Date: Sun, 10 May 2026 22:57:46 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Language: en-US To: Peter Zijlstra , Juri Lelli , Sasha Levin Cc: regressions@lists.linux.dev, stable@vger.kernel.org, linux-rt-users@vger.kernel.org From: Lukas Beckmann Subject: [REGRESSION] 6.12.y: d66792919d4f (sched/deadline: Use revised wakeup rule for dl_server) causes latencies up to 50ms with PREEMPT_RT Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-MBO-RS-META: 819ydxywk7c5su85wrfixtgzefupgtru X-MBO-RS-ID: 69f2eb288b23dbea7ee Hi, 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) cyclictest results on the current linux-6.12.y branch (tag v6.12.87): # /dev/cpu_dma_latency set to 0us policy: fifo: loadavg: 9.37 9.21 6.90 9/211 978 T: 0 ( 884) P:80 I:250 C:4688252 Min: 3 Act: 6 Avg: 6 Max: 51956 T: 1 ( 885) P:80 I:250 C:4688051 Min: 3 Act: 7 Avg: 6 Max: 50106 T: 2 ( 886) P:80 I:250 C:4688242 Min: 3 Act: 6 Avg: 6 Max: 51965 T: 3 ( 887) P:80 I:250 C:4688434 Min: 3 Act: 12 Avg: 8 Max: 59 cyclictest results on 6.12.y with d66792919d4f reverted: # /dev/cpu_dma_latency set to 0us policy: fifo: loadavg: 9.43 9.50 9.44 8/204 5758 T: 0 ( 862) P:80 I:250 C:272329322 Min: 3 Act: 6 Avg: 6 Max: 57 T: 1 ( 863) P:80 I:250 C:272329324 Min: 3 Act: 7 Avg: 6 Max: 77 T: 2 ( 864) P:80 I:250 C:272329322 Min: 3 Act: 7 Avg: 6 Max: 68 T: 3 ( 865) P:80 I:250 C:272329322 Min: 3 Act: 16 Avg: 7 Max: 81 This is reproducible on multiple machines. It looks like the timer fires and there is also a sched_waking event in the trace, but the cyclictest thread does not get scheduled for another 50ms. 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 with testing if needed. Thanks Lukas Beckmann #regzbot introduced: d66792919d4f