From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3494C433F5 for ; Fri, 10 Sep 2021 04:14:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CB99D60FDA for ; Fri, 10 Sep 2021 04:14:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230145AbhIJEQE (ORCPT ); Fri, 10 Sep 2021 00:16:04 -0400 Received: from mout.gmx.net ([212.227.17.20]:39079 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229462AbhIJEQD (ORCPT ); Fri, 10 Sep 2021 00:16:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1631247284; bh=rVhS98kJuXOnQaP7kFU1p2+ZpKPQj1X3psyXiI/RJPw=; h=X-UI-Sender-Class:Subject:From:To:Cc:Date:In-Reply-To:References; b=k7cNoLKduf3CbFZ+DBR2k5ZUz/lnn3roEJzz7udeLJq2kce5dAPiuELyYIMin1MVK 4X8rQ06rvWUXWJVE6HJ/l6Agz4ieoKrngvqDkZQ5FUXqN/TytJEHr8QYCXeQVzX+jY RNyvCGtLY0IsZYNOlqbp4K+Kes+MxiMpRoQPmHnM= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from homer.fritz.box ([185.221.151.43]) by mail.gmx.net (mrgmx105 [212.227.17.168]) with ESMTPSA (Nemesis) id 1Mqb1c-1mkQLM3CAi-00md8r; Fri, 10 Sep 2021 06:14:44 +0200 Message-ID: <817e71d3987224bbacfd916b2d953fb528ecb4d5.camel@gmx.de> Subject: Re: question about isolcpus and nohz_full From: Mike Galbraith To: Chris Friesen Cc: Frederic Weisbecker , LKML Date: Fri, 10 Sep 2021 06:14:43 +0200 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.41.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:HnBSxbAoExudxLQpb9sxZIRqna151B5g7WT8YRL5SJpE0Ct+kH8 1OfHlbK96BwBVQ4MFoeJSF5mynf2o6O8KHoIvSOFdOeOGk+qoUSeTIj9+OilH0wPKqbtIqC 1dIQhI9s6vkKxLecK8Omuq60HJBKxgCv2hPrlh44gvH5/su1RPXKKSwqJsj8OWZroOXrDFu jnoZe9J92M3oYf1AwOquQ== X-UI-Out-Filterresults: notjunk:1;V03:K0:8mbqzdPw2/Q=:CIw/2qX3eUZX4tdXIBY5Yx CyAKaSb40Iinr2MR+IBF7ChsGedEbP56KZ5Ya4nZSdQggjmpFlB3jPVcqN1du8Sadh1PpgxPJ alfBh6O402Uy7PeeRm9P8TTEbn8czjJeg4iyHLMtISjM2EVqQnLPGqkvSu4RJZTV6m02q1mE4 0vYcBujUklVFq0Q3OInZ2Erb8jXNQvNFFt7tVMqHhuPfOfydLXfbTfn5mdlh/aU5Uu+2gRCrQ 3rHPW0mo4la4uBTAN/XbqTYTcIHkuGWj963a4RgNgQCEsWhS9qnL+rZ9qJcXLborWuy+dClFC SEZ/0QG8ArORxjWpjQyOeIBvj8kgj8Xy4JKqYMYLN8JrQIFvi0euLK9GtTJZGA6WSgeTfQbcz F+jkihRrfe9AysMDHmXPvKuak7VR9iMn+tKmM3K5TKdHdA5dVYR0w4KvPLDypEiDqDs5lGSmw 536DVrBhg8gK5XeGbUKcaZmTrRQ/kWXvuv80WWmPCJkBBL2TqW7MjQJUIv3HGDsy+XUOSuvBH BjQe3bAjaystWqTkJtYbXmMSe9S09KLa6e9Nh6RLt71lgniF3K0C8L5lI14cRNbCSOyFkcbZM E+0xfOWRHxQL/kCiCKI5nbgD4EJMCeTR0PxIohVvjkgrskxSZnBZaFEWwKOuMbrO0/vTFGROX aax4W0FjgEgfMNmIGOYTWraLzAnGCKm0hxiOC+maZCw3Rzi0gZiZbp+1IPaG7LKTWe/VPvHBO 5tjIgnhHtUCtBzlDmpaOXzwp0F3MiusjpHsFsFKAPppITq/K9kN7k/QfSEMkwdScxc5KR5U5v wfuRbjm4CrCU0qzR52LFYu2RSiNH+jAU2nQQn5k5PsezTvMqPqidamZ8dq1pCYjWn1PgVXi+p +AMhPwXTQyAQgl1KHvERJzIggP8EvTWMR3E+aSz+5rtb2n2+IRztmLQWty+qdFgMybzHsBJgS mIXGc1WrVHnBuS+l6LDsgb8HfWLg3U0C6EfUtCbDmyYu5SCZLe17OlVzvIvcjk4ugyoxWT7hK lT8cFdGLvNIrjoJQ079fHmzmCgUFIgdJZQV3jWtThyUIuf43R6FHbEc+U8712SuySMAurgdEV fcSrr2QJn55X7Q= Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2021-09-09 at 10:26 -0600, Chris Friesen wrote: > > 2) Is it allowed to specify=C2=A0 "nohz_full" for some CPUs at boot time > without specifying any isolcpus? Yup (IM[not the least bit;]HO the proper way to partition a box). > =C2=A0 If so, what happens if I later isolate > a subset of those CPUs using "cpuset.sched_load_balance" in cgroups?=C2= =A0 Is > that allowed when the equivalent boot args are not? That's what an old shield script I still have laying around does. I booted master on my little desktop box with nohz_full=3D1,2,3,5,6,7 and shielded cores 2 and 3, after taking down cpus 4-7 (smt), and it still seems to work fine. I used to also override (via ugly.. maybe even fugly, hack) nohz dynamically, turning the tick on/off for subsets, on having proven best for jitter of heftily threaded RT app spread across many isolated cores, thus could at need even partition a box with a mixture of ticked, nohz idle, and tickless sets, albeit in a rather limited fashion due to nohz_full preallocation requirement. Would be nice for some situations if nohz mode were to become a fully dynamic set attribute. -Mike