From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 5E7263603D8; Thu, 21 May 2026 16:49:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779382195; cv=none; b=pQ6vC4ll66PD7eBhenHjqWRMGqxvJQibLMFPcKE6MKTzJ1yZEwOT7yvViV7hlcqL1SvPlR6JMcUcBR0CSP7TkS7h4ZCS0VHIudTOa6oDFIOHE7SYczSxWcFiEft/e6rv3jgHfYu2Cp7OJVpoE5eDTy9ib0Mw57RVsiLGpCs7dFE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779382195; c=relaxed/simple; bh=OprqkZ4QQ6aVcqoi38f9+g2AKha6qufljc9vtGYMfqk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WGPnrsnCnpV7GsI/4zxIpgazlITHOmYlvyv6ygCqghFTcbRgwFDyv7v3DUoxK6IxIBTlWZ67DXBOZsbaWFuvES23q3heT4nmh7ttiWSYuNBolq45Zz0kJLjOB+MSq1rP8zXymjzZDgyAg/c53Ub8dy7mF4X3CfG6udTQhYJTbpo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=C1qFyy0g; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="C1qFyy0g" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ADE311F000E9; Thu, 21 May 2026 16:49:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779382194; bh=OUnA3Q5Ym/N4yLTZMCcZsZgJO5BwUC8CzQvcJOviwDo=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=C1qFyy0garECdj4RrDdLmtTsE5zyEKLrJwhvLJJDQGG6+Amej/CsxdhoyvJiuZ8lC yD0dkjofznnGkryOOQeazv1o+HJ7ByGf9WrIhn2iFvaUGU/1JPP5GLUkZLmrf9Q3IO VCWZPpwrCHQNfwk0ezSLZfplsGTd9zO5s4hmxjdAlkczEEtpjt6lKwyFVj6kV4SFSb oLiGcaR1ETX1kkx/bhnDcP+s9xW2ezqpZII82RrBW/q2U/zlVaTqzLt41X4QpADQc3 uzf6qqppfyzkaEyi/aqXoBvuw2oQ1BsveF9iXdxOXmbwsE0dwPFLE9MkuNqQScBjQN Hc97FCR666WYg== Date: Thu, 21 May 2026 12:49:52 -0400 From: Sasha Levin To: Thorsten Leemhuis Cc: regressions@lists.linux.dev, Juri Lelli , Peter Zijlstra , stable@vger.kernel.org, linux-rt-users@vger.kernel.org, Mike Galbraith , Lukas Beckmann Subject: Re: [REGRESSION] 6.12.y: d66792919d4f (sched/deadline: Use revised wakeup rule for dl_server) causes latencies up to 50ms with PREEMPT_RT Message-ID: References: <04657838-46d1-432d-95e1-eb73b930b032@mailbox.org> <20260511141441.stable-reply-0001@kernel.org> <4e31e3b5-fa69-4c4c-a5e9-dea7a8452ee7@mailbox.org> <36acb7e8-1fae-4c6d-8145-a29685007a76@leemhuis.info> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <36acb7e8-1fae-4c6d-8145-a29685007a76@leemhuis.info> On Thu, May 21, 2026 at 09:32:32AM +0200, Thorsten Leemhuis wrote: >On 5/16/26 21:50, Lukas Beckmann wrote: >> On Tue, May 12, 2026 at 12:08:49AM +0200, Lukas Beckmann wrote: >>> On 5/11/26 16:21, Sasha Levin wrote: >>>> Thanks for the detailed report. Before I revert d66792919d4f from 6.12.y, >>>> I'd like to confirm whether the underlying issue is the missing dl_server >>>> rework chain on 6.12.y rather than the revised wakeup rule itself. >>>> >>>> Mike's reply notes that his local 6.12-rt tree carrying the following >>>> three commits in cannot reproduce, while the same tree without them >>>> reproduces quickly: >>>> >>>>    cccb45d7c429 ("sched/deadline: Less agressive dl_server handling") >>>>    4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck") >>>>    a3a70caf7906 ("sched/deadline: Fix dl_server behaviour") >>>> >>>> d66792919d4f's upstream commit message explicitly says it relies on the >>>> state established by a3a70caf7906, and none of the three are in 6.12.y. >>>> >>>> Could you give those three commits a spin on top of 6.12.y (keeping >>>> d66792919d4f in place) and see whether the latency goes away? >>> >>> If I apply the three commits on 6.12.y, the latencies indeed go away. >>> This is running for a few hours now, and the latencies showed up after 30 >>> minutes tops, with plain 6.12.y before. >>> I will leave this running. >> >> Cyclictest is still running and looking good (latency-wise). >> How should we proceed? > >Sasha, just wondering: is this still in your queue? It sounds like a >clear case to pick those three up for 6.12.y (everybody: please correct >me if I'm wrong). Or are you busy and should we ask Greg to pick them up? Nope, sorry, I got sidetracked by a large series of commits from the merge window. I'll plan to queue this up for the next release. It'll be even better if someone can send us a more "official" backport request, ideally with a tested-by too :) -- Thanks, Sasha