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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 CE997C388F7 for ; Tue, 10 Nov 2020 15:32:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6613720795 for ; Tue, 10 Nov 2020 15:32:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cUKAIFuH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730985AbgKJPcN (ORCPT ); Tue, 10 Nov 2020 10:32:13 -0500 Received: from mail.kernel.org ([198.145.29.99]:34518 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730666AbgKJPcM (ORCPT ); Tue, 10 Nov 2020 10:32:12 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BE7172076E; Tue, 10 Nov 2020 15:32:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605022331; bh=K8VDqFdwKyqA5Y+dk5hxgwCzE73NJ2L201GMD5MtvM4=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=cUKAIFuHhEVNGDkyQhX0/0PFsVhuyVsW6jOBKvmQyyEsUcsqjIV+Isdq32WM4nFf6 YSYVcRUuHFKsuSYVJPoVOxOC4bBi2XGgMdAtwkdA4ZsAKEMiA8cs9qzjRDIOBh7jzh ijck5y3HvRUwYrotWhZlntHnEbufKa9nzkc/7vo0= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 5723F35226CB; Tue, 10 Nov 2020 07:32:11 -0800 (PST) Date: Tue, 10 Nov 2020 07:32:11 -0800 From: "Paul E. McKenney" To: Paul Gortmaker Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, rdunlap@infradead.org, colin.king@canonical.com, Frederic Weisbecker , Josh Triplett , Thomas Gleixner , Ingo Molnar , Li Zefan Subject: Re: [PATCH v2 0/4] support for global CPU list abbreviations Message-ID: <20201110153211.GU3249@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201110040725.1478297-1-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201110040725.1478297-1-paul.gortmaker@windriver.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 09, 2020 at 11:07:21PM -0500, Paul Gortmaker wrote: > RFC/v1 ---> v2: > > commit #1: > leave one line stub behind for !SMP solving build failures. > Reported by Randy Dunlap and various build bots. > > commit #4 > manage to remember '\0' char in strlen from one line to the next. > Reported by Colin King. > > Original description from v1/RFC below remains unchanged... Queued and this time kicking off testing that actually includes your patches! ;-) Thanx, Paul > --- > > The basic objective here was to add support for "nohz_full=8-last" and/or > "rcu_nocbs="4-last" -- essentially introduce "last" as a portable > reference evaluated at boot/runtime for anything using a CPU list. > > The thinking behind this, is that people carve off a few early CPUs to > support housekeeping tasks, and perhaps dedicate one to a busy I/O > peripheral, and then the remaining pool of CPUs out to the end are a > part of a commonly configured pool used for the real work the user > cares about. > > Extend that logic out to a fleet of machines - some new, and some > nearing EOL, and you've probably got a wide range of core counts to > contend with - even though the early number of cores dedicated to the > system overhead probably doesn't vary. > > This change would enable sysadmins to have a common bootarg across all > such systems, and would also avoid any off-by-one fencepost errors that > happen for users who might briefly forget that core counts start at > zero. > > Looking around before starting, I noticed RCU already had a short-form > abbreviation "all" -- but if we want to treat CPU lists in a uniform > matter, then tokens shouldn't be implemented at a subsystem level and > hence be subsystem specific; each with their own variations. > > So I moved "all" to global use - for boot args, and for cgroups. Then > I added the inverse "none" and finally, the one I wanted -- "last". > > The use of "last" isn't a standalone word like "all" or "none". It will > be a part of a complete range specification, possibly with CSV separate > ranges, and possibly specified multiple times. So I had to be a bit > more careful with string matching - and hence un-inlined the parse > function as commit #1 in this series. > > But it really is a generic support for "replace token ABC with known at > boot value XYZ" - for example, it would be trivial to extend support to > add "half" as a dynamic token to be replaced with 1/2 the core count, > even though I wouldn't suggest that has a use case like "last" does. > > I tested the string matching with a bunch of intentionally badly crafted > strings in a user-space harness, and tested bootarg use with nohz_full > and rcu_nocbs, and also the post-boot cgroup use case as per below: > > root@hackbox:/sys/fs/cgroup/cpuset# mkdir foo > root@hackbox:/sys/fs/cgroup/cpuset# cd foo > root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > > root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-last > cpuset.cpus > root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > 10-15 > root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo all > cpuset.cpus > root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > 0-15 > root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo none > cpuset.cpus > root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > > root@hackbox:/sys/fs/cgroup/cpuset/foo# > > This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file. > > Note that the two use cases (boot and runtime) are why you see "early" > parameter in the code - I entertained just sticking the string copy on > the stack vs. the early alloc dance, but this felt more correct/robust. > The cgroup and modular code using cpulist_parse() are runtime cases. > > --- > > Cc: Frederic Weisbecker > Cc: "Paul E. McKenney" > Cc: Josh Triplett > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: Li Zefan > > Paul Gortmaker (4): > cpumask: un-inline cpulist_parse for SMP; prepare for ascii helpers > cpumask: make "all" alias global and not just RCU > cpumask: add a "none" alias to complement "all" > cpumask: add "last" alias for cpu list specifications > > .../admin-guide/kernel-parameters.rst | 20 +++ > .../admin-guide/kernel-parameters.txt | 4 +- > include/linux/cpumask.h | 8 ++ > kernel/rcu/tree_plugin.h | 13 +- > lib/cpumask.c | 132 ++++++++++++++++++ > 5 files changed, 165 insertions(+), 12 deletions(-) > > -- > 2.25.1 >