From nobody Mon Feb 9 01:50:24 2026 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 D3EDE2F46; Wed, 5 Feb 2025 03:03:12 +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=1738724593; cv=none; b=NoRbxnZI3lTzXDgl/72WXFqi1zt6dz1ZNarNG4yT5J9m9zbuqb9jtEAG/HUJijNsDjve4yN3fIMtjSnLwhElwlhuRE9KEZ52t+6e7ZvDH6y0UcJjvfCM1k9n7FvCfMKBhUniJGUFAvaMpiur8KRGDIrwkwYqtHUTpaGn+nJ4H7M= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738724593; c=relaxed/simple; bh=g6XqJi+3efzE8zFPlaanW3f9Ug9ugh+JBc0KjXvtBU4=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=Xvc8yIFggLxjqJboAI/pFQTqLi7dSLZmymtXwSECCRqoEl8wYOaG1DUrLjDOPW0vEogSsVHI24mkzIpSItEEksXAhIa+S2/XUaFNrpRDv7J4zjl+1zlLVE1H/CBlWOvhuWysMPxz5OZBkztd240yEeBOa2iY3Sw7GHBgU1Ba/wQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nxEBMQ1O; 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="nxEBMQ1O" Received: by smtp.kernel.org (Postfix) with ESMTPS id 3F6F3C4CEDF; Wed, 5 Feb 2025 03:03:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738724592; bh=g6XqJi+3efzE8zFPlaanW3f9Ug9ugh+JBc0KjXvtBU4=; h=From:Date:Subject:To:Cc:Reply-To:From; b=nxEBMQ1Otzbfr8Miy8itzaRuIqZcBtTIS5iDE1E6wSKs74Ttx1ATEpl+6dRt+0R8X sm99GN4lVBq3IU7w1Ddn7eNxrshzpZQ1ATHV440zSF2s9ep4NhSzHe39I4MFZEBKm1 mEk51fn1ExWrTDE1WbH6RSnopx1/R1/KBf3WHBw0S4lQnhCR8NDLM4LnmQlwMX7L+X gmoQNW5knlpPqZejpRPb8n1sMYs01FfTutAG4nvf+QX41FzgDCx8GdXZ6JhD1DAslB vRD4fadAIjuww39fJ3QFUVRERbo1yUCG3g2UkHi6QtLNoYZn0N8dnLR5259/EH54Fm 6oVozAZYZp19g== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id 30CDFC02193; Wed, 5 Feb 2025 03:03:12 +0000 (UTC) From: Krishanth Jagaduri via B4 Relay Date: Wed, 05 Feb 2025 08:32:14 +0530 Subject: [PATCH] Documentation/no_hz: Remove description that states boot CPU cannot be nohz_full Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250205-send-oss-20250129-v1-1-d404921e6d7e@sony.com> X-B4-Tracking: v=1; b=H4sIALXUomcC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDI1MDQyNL3eLUvBTd/OJiXbiIcbKJUUpymomZcWqSElBfQVFqWmYF2Mzo2Np aANx8/qJjAAAA X-Change-ID: 20250129-send-oss-20250129-3c42dcf463eb To: Thomas Gleixner , Jonathan Corbet Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Atsushi Ochiai , Daniel Palmer , Oleg Nesterov , stable@vger.kernel.org, Krishanth Jagaduri X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1738724552; l=2701; i=Krishanth.Jagaduri@sony.com; s=20250122; h=from:subject:message-id; bh=E835T3tqOhFIcn/Jm6X5qlETpMAWcMeplxvdOyEAeTk=; b=arldPplnu5QfSI/nuErJEq7UekxDqNZEtHWhOuNB63444+4wrmK/5cLfNDHZOvmrYyCnN/vOn GO55gjfsmhvDDyu1ZDrKcb7qOBtL1+NorXtzZGYZXpdTPdiNYzmlqQ0 X-Developer-Key: i=Krishanth.Jagaduri@sony.com; a=ed25519; pk=lx2tvWPqsnFN2XCeuuKdm7G2bXm/Grq1a1KTsSpFZSk= X-Endpoint-Received: by B4 Relay for Krishanth.Jagaduri@sony.com/20250122 with auth_id=326 X-Original-From: Krishanth Jagaduri Reply-To: Krishanth.Jagaduri@sony.com From: Oleg Nesterov [ Upstream commit 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e ] Documentation/timers/no_hz.rst states that the "nohz_full=3D" mask must not include the boot CPU, which is no longer true after: commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full"). Apply changes only to Documentation/timers/no_hz.rst in stable kernels. Signed-off-by: Oleg Nesterov Cc: stable@vger.kernel.org # 5.4+ Signed-off-by: Krishanth Jagaduri --- Hi, Before kernel 6.9, Documentation/timers/no_hz.rst states that "nohz_full=3D" mask must not include the boot CPU, which is no longer true after commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full"). This was fixed upstream by commit 5097cbcb38e6 ("sched/isolation: Prevent boot crash when the boot CPU is nohz_full"). While it fixes the document description, it also fixes issue introduced by another commit aae17ebb53cd ("workqueue: Avoid using isolated cpus' timers on queue_delayed_work"). It is unlikely that it will be backported to stable kernels which does not contain the commit that introduced the issue. Could Documentation/timers/no_hz.rst be fixed in stable kernels 5.4+? --- Documentation/timers/no_hz.rst | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst index 065db217cb04fc252bbf6a05991296e7f1d3a4c5..16bda468423e88090c0dc467ca7= a5c7f3fd2bf02 100644 --- a/Documentation/timers/no_hz.rst +++ b/Documentation/timers/no_hz.rst @@ -129,11 +129,8 @@ adaptive-tick CPUs: At least one non-adaptive-tick CP= U must remain online to handle timekeeping tasks in order to ensure that system calls like gettimeofday() returns accurate values on adaptive-tick CPUs. (This is not an issue for CONFIG_NO_HZ_IDLE=3Dy because there are no runni= ng -user processes to observe slight drifts in clock rate.) Therefore, the -boot CPU is prohibited from entering adaptive-ticks mode. Specifying a -"nohz_full=3D" mask that includes the boot CPU will result in a boot-time -error message, and the boot CPU will be removed from the mask. Note that -this means that your system must have at least two CPUs in order for +user processes to observe slight drifts in clock rate.) Note that this +means that your system must have at least two CPUs in order for CONFIG_NO_HZ_FULL=3Dy to do anything for you. =20 Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded. --- base-commit: 219d54332a09e8d8741c1e1982f5eae56099de85 change-id: 20250129-send-oss-20250129-3c42dcf463eb Best regards, --=20 Krishanth Jagaduri