From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 27B583D9DD7; Mon, 11 May 2026 14:21:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778509320; cv=none; b=FLOgFh/oaGrDQG2MhiJKxi++oavGS0d14FrksrqQA5wQIfL7t8DJm8erC2Ju5PAWo9nWrk8dqVWE1iADNkfw25gXwqAkjC0Gi/+jg85N0jQKhO6cu/TFfe+Oh2837cDADsCT4xtRf+aZg57pJYZpBwrgi4jK/eeq1E8rBn70gBQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778509320; c=relaxed/simple; bh=UWwlvz/FBg65FNAhHu+MP/kqeZ/hILQT6+2DtYu8mYE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CzTWnHYnZXsyHACELya63EyzSK8RyaqCbPFF5Ol+hnTaQDtQ2mu0NHuSholkSimPVbK9+IfeSJZUNaHAcBx+df0wKdDEGvZDITZwkmQGp2Vxml20I7HQcppuHhH/VPpzZP04DMRNFS8PLCi2hZu1/HKbaH+wHKpFDaI4A7XWh50= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=S6/mdimA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="S6/mdimA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DCF1DC2BCF7; Mon, 11 May 2026 14:21:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778509319; bh=UWwlvz/FBg65FNAhHu+MP/kqeZ/hILQT6+2DtYu8mYE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=S6/mdimA/Varc6IDGxnvDIUXKWhsf+TjpoEuSUKTty5eHbDf3BHRJ05RVz0nbrw2l JKM2EUD5ZGAy4owhWqPD8rfRwXjNfr7v6AlMulsyuHNMZNZ53Y11hFAaN8Mf+l6s8u qrUuKTtiINSIrMhG3O4u833YpyF5F3lHFk6WFM0X5HzPNcf3xfB1tL7jbicc/xSYko TjW5/YrbyjUnZgS5EIRzR66K1m+Cy/rJwvWiO3G8Ks+1+2vLR6x1uMmkpKYfSIcIu1 dlQKOlFGBMMfqoYxy76aBvdh2medwWbFkRXd+98QUTyom97t9igqIgtvAKkIZOYmhz wHXnwSgla+SIw== From: Sasha Levin To: Peter Zijlstra , Juri Lelli Cc: Sasha Levin , regressions@lists.linux.dev, stable@vger.kernel.org, linux-rt-users@vger.kernel.org, Lukas Beckmann , 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 Date: Mon, 11 May 2026 10:21:50 -0400 Message-ID: <20260511141441.stable-reply-0001@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <04657838-46d1-432d-95e1-eb73b930b032@mailbox.org> References: <04657838-46d1-432d-95e1-eb73b930b032@mailbox.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Sun, May 10, 2026 at 10:57:46PM +0200, Lukas Beckmann wrote: > 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. [...] > Is it possible to revert the commit? > > I can provide traces or help with testing if needed. 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? -- Thanks, Sasha