From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793282537; b=ZbmJCcl+bo8Til7SD8n+G/jwTzOYEIBoCaeYvQQbsUgoLyOdOLrPYCcXwAYN5rUBEw+B V7WPGE+ADOfezLyvdQ4S1TfHMp8kbIMGu36ezLG+GLdNXDFASSVc+rMj1y1ynYE/aSf8u dE9qR46cQ8vXiMSeaszvr98Up9m/zNBscSBPDWCkuEFtH5rm7xeu14zR1UZVq6xky2+hu 7m+jb06ssa4vnLxp4yb+Ac0svnmzDXPiz0ndeNSF0EL4UaORHCDCUaMcgHBMSH5/VBKJl m6Hm2sjuWrI6ab9Cx3zjuZAvXq9+G9jmSX/rB2gYf968xhWcfU2m+KXi4l85z2scvHg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793282537; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition: Content-Transfer-Encoding:In-Reply-To; bh=sw9b5i5WLSBIXyPstV+YM76/P9T1C9sWYcZnq+XWeW0=; b=O7eQS2XN77u7DgyRsMYQVnO6h0Pmjh74Ijq48k4n52IyCno39idoQ1S2+aJTmiFZaqYv /n9ucrxgZPCwYY4e07poG3n04JkuM09fy8nJAQJ9bArCSw3Rn1CUX+oHY2CkNaVHhHbuh FeW5/jT1tjdKEQlT6kYv+zWsZqQxnY0oh0taGtKm4RaRbwLfwy6a+ROZ70TCep9mCkx/u Bz/+aFjN8WhYLo1c6znTjLtsZwKh8dyQKwRbNSAjeU/kVdmcf99yfpqkiA14xtyFUgCG+ IlkXt2hIfkPb7sKPZxGoyU7TizkSYM7Rwhv0bsRImB6EqBiJ4/HqkaTnJrNHKJTIisw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=MC1JJf+V; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F406D606A31D; Thu, 29 Oct 2026 14:02:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=MC1JJf+V Received: by smtp.kernel.org (Postfix) with ESMTPSA id 12AA71F01825; Thu, 29 Oct 2026 14:02:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793282536; bh=sw9b5i5WLSBIXyPstV+YM76/P9T1C9sWYcZnq+XWeW0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=MC1JJf+Vgr7VTcro43Hgd+be34yLuBACy41tB9UT8aTU/+EzRekP8IF/K/vKujBbI PJvcYGlmTu9Fruo1jhk/qornxAqtHRSM8NZuIK3SA7KLLm66sEgQVIiQ1P+xWqKgFC 4JH1WO/i0OV3hp8z1h80pHFrxoEbWqKerj//C+3RJKk2lQOY5aKVNgagqClCY9uHKk 9rBgUhfTq01/ibUK7j/aWeW9Xd2E2YyQWawwcu5/msyJtiojL8JTRoTcXndFKVQpZn 8fJ7CLymIVVGhnF8jX2GJKXGHvAghDcsqzjNN/OsVdpeoFx0FJdS6Q71CJDpkMzQ3s RDWgG3ZxcRKmA== Date: Thu, 29 Oct 2026 15:02:13 +0100 From: Frederic Weisbecker To: Peng Wang Cc: Anna-Maria Behnsen , Ingo Molnar , Thomas Gleixner , Greg Kroah-Hartman , "Rafael J . Wysocki" , Danilo Krummrich , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Peter Zijlstra , Waiman Long , Tejun Heo , He Rongguang , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, driver-core@lists.linux.dev, linux-trace-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [RFC PATCH v2 1/2] tick/nohz: Add a policy dependency for full dynticks Message-ID: References: <58bc33cb018a2651e9cc3fc02baad7de4d543705.1792242566.git.peng_wang@linux.alibaba.com> X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Le Thu, Oct 29, 2026 at 02:41:28PM +0800, Peng Wang a écrit : > Hi Frederic, > > > Do you mean that your database runs better when hosts CPUs are in nohz_full? > > Yes. In our database tests, suppressing the host's non-idle > periodic tick improved performance, with the rest of the host > configuration unchanged. Out of curiosity, for such database tests, only the host tick is off, not the guest tick, right? > > But how does this new interface help? Ie: why is it worse to have all CPUs in > > The tick policy itself can therefore affect guest performance. > A large host runs VMs for many customers with different workloads. > Customers create and release VMs independently, so the same host > CPU can be reassigned to a different workload while other VMs > remain running. > > We want to choose whether to retain the non-idle tick or allow its > suppression for the workload currently assigned to each CPU, and > revisit that choice when the CPU is reassigned. Per-CPU control > lets us do this without rebooting or taking CPUs offline. Ok in that case, do you know about the current work in progress to make nohz_full opt-able through cpusets? It implies taking the target CPUs offline shortly but the policy is to be setup before VM is launched, right? Thanks. -- Frederic Weisbecker SUSE Labs