From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-102.mailbox.org (mout-p-102.mailbox.org [80.241.56.152]) (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 1278238A299 for ; Fri, 22 May 2026 21:35:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.152 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779485750; cv=none; b=VEna0FbU80Sgkl4bgNxt2H48C79zI1CWeVPtnETkjsK02iBbgIBov4kYULjxToaZb0rmB+acmWu70B0DDDoHyc82TiDHn4EycmzRtmDDZmsTZSITmBRLWzpe0nUahFNVsLKMrFl6/8FmJAQKmI0uu3vnFWZFUrlv+k/lxtBa4lY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779485750; c=relaxed/simple; bh=6mqs19zcjW9MPMkLIEWnJ6K3J4xE3leiRLzVL6gy9Uw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rQGF7uYz3PTAFoY9LNB/5yA3+Ouw79r9GWCtTR8vCsQBCWRng+qBdPNgu/4c9ETiC7OS714Fa7MNVM91RmtoC6muVSor52UBzZGOsgm2d/FvVZBR8teXPu2V+72rK4jCw2DDCzXeTFpPUikjzzWQEuZ+GhmuRcxcxJLUeklgPGY= 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=QpcEkhP/; arc=none smtp.client-ip=80.241.56.152 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="QpcEkhP/" Received: from smtp102.mailbox.org (smtp102.mailbox.org [IPv6:2001:67c:2050:b231:465::102]) (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-102.mailbox.org (Postfix) with ESMTPS id 4gMdqj22g7z9vGS; Fri, 22 May 2026 23:35:45 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1779485745; 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: in-reply-to:in-reply-to:references:references; bh=0cb50XGJqdLe/0Jbg6NNuje/yLxMm8hagq02OE3Rdbc=; b=QpcEkhP/AxRarMUUWElJHqIgwT4lpnGmNAnJhySUZjjy5tBibgkuL1ksmYlCy62K877bxI WEPgVVmEOl3Q4juRR7JV/XBiXy1LyiSv/6PA7nkGx5l0lTBgbnq7VkrknLHwWhttUh6Ne8 fOvAbN4GoFYAhjC5e66AATpLOGTjrPI1M+LmjrEJROxs47OXLIovqW+1XBz4cHQr84BlUT HlHE6IK6W7QyEI9eIyRURFptIhfKVBWsnOq6irfl2MJFH8lIZOo5dRFW6OLGj8ovft8Oza 50/1j10nxgJZvS1Z5lWEPxGZvaUNTOsq/ucMvl1aFtDaUk1LHeTeG46sJ8llWA== Date: Fri, 22 May 2026 23:35:35 +0200 From: Lukas Beckmann To: Sasha Levin Cc: Thorsten Leemhuis , regressions@lists.linux.dev, Juri Lelli , Peter Zijlstra , stable@vger.kernel.org, linux-rt-users@vger.kernel.org, Mike Galbraith 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: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-MBO-RS-META: yp6io1r5ek3qkuj7awrr571p6w9jzziz X-MBO-RS-ID: a03349e21277d638757 On Thu, May 21, 2026 at 12:49:52PM -0400, Sasha Levin wrote: > 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 :) Done in https://lore.kernel.org/stable/20260522213120.1205100-1-lbckmnn@mailbox.org/ > -- > Thanks, > Sasha Thanks, Lukas