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=-12.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 87E56C433E0 for ; Mon, 22 Feb 2021 23:44:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CEF664E05 for ; Mon, 22 Feb 2021 23:44:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231438AbhBVXoI (ORCPT ); Mon, 22 Feb 2021 18:44:08 -0500 Received: from mail.kernel.org ([198.145.29.99]:54290 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230088AbhBVXoF (ORCPT ); Mon, 22 Feb 2021 18:44:05 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2762E64E00; Mon, 22 Feb 2021 23:43:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614037404; bh=gJMms421b5cvbD5M9HvPWUC+099Pr/G7QIjdPJ3ZCgY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=iImD1sVhKc2Obnx1+gPxf93iJNt3PzkZ70wPdlZgIYS97P0y9u3ApcrQqpWT7jiSh NRcQiwheD7jxd/9d9VYqvdZ7WKx3oJEZJGhzW4bs8i4Q+URcBW4iAypCvO/H7NmkfL h7h0No192BEDzllQcTqWMmKu+kXtXsv8+dCE9NoTECdoZtSc+TJjnHr9b8YW0VORFE BBfZiiFACtbSTFXDMeY6A3kCrINrH5RD8w7uXcOnB0vhLPkgh8dej2MljgwklVId0m usekEGTb1z+rQ/NyzE7qCkbVwsDwa8jrUGwFDXkvNL8n2z3Xr4hEX8FCRiahHXK3nO ZOSo4GQEWG6aw== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id EB11E3523031; Mon, 22 Feb 2021 15:43:23 -0800 (PST) Date: Mon, 22 Feb 2021 15:43:23 -0800 From: "Paul E. McKenney" To: Paul Gortmaker Cc: linux-kernel@vger.kernel.org, Li Zefan , Ingo Molnar , Yury Norov , Thomas Gleixner , Josh Triplett , Peter Zijlstra , Frederic Weisbecker , Rasmus Villemoes , Andy Shevchenko Subject: Re: [PATCH v5 0/8] support for bitmap (and hence CPU) list "N" abbreviation Message-ID: <20210222234323.GR2743@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210221080827.84862-1-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210221080827.84862-1-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 Sun, Feb 21, 2021 at 03:08:19AM -0500, Paul Gortmaker wrote: > This is the 5th and final version of this series. We got some good > improvements, like adding self-tests, using "N" as "just another number" > that could be used anywhere, and making things not CPU specific. > > But now it is time to close this review out since is down to just > hand-wringing over hypothetical use cases, bikeshedding on upper/lower > case, and a wild goose chase on trying to avoid adding a function arg. > > So, once again - thanks to all who provided input; it was all considered > even if not all of it was used. And in that vein, just to be clear: > > 1) There will be no adaptive modifying or guessing what the user meant if > a range turns out to be invalid. The caller will be responsible for > handling the -EINVAL just as things are currently today. > > 2) There will be no use of "L" or lower case "n" because there is simply > no need for it. Yes, it would be simple enough to add, but it complicates > things and would also be impossible to remove later, once it went mainline. Queued and pushed, thank you!!! Thanx, Paul > The original text from v4 follows: > > The basic objective here was to add support for "nohz_full=8-N" and/or > "rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference > to the last core, evaluated at boot 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. > > Originally I did this at the CPU subsys level, but Yury suggested it > be moved down further to bitmap level itself, which made the core > implementation smaller and less complex, but the series longer. > > New self tests are added to better exercise what bitmap range/region > currently supports, and new tests are added for the new "N" support. > > Also tested boot arg and the post-boot cgroup use case as per below: > > root@hackbox:~# cat /proc/cmdline > BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2 > root@hackbox:~# dmesg|grep Offl > rcu: Offload RCU callbacks from CPUs: 2-3,8,10,12,14. > > root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > > root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus > root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > 10-15 > root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus > root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > 15 > > This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file. > > Note that "N" is a dynamic quantity, and can change scope if the bitmap > is changed in size. So at the risk of stating the obvious, don't use it > for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff. > > Paul. > --- > > [v5: go back to v3 location of "nbits" in region. Add acks/reviewed.] > > [v4: pair nbits with region, instead of inside it. Split EINVAL and > ERANGE tests. Don't handle start/end/offset within a macro to > abstract away nbits usage. Added some Reviwed-by/Ack tags.] > https://lore.kernel.org/lkml/20210209225907.78405-1-paul.gortmaker@windriver.com/ > > [v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs. > just being allowed at end of range like "0-N". Add new self-tests. Drop > "all" and "none" aliases as redundant and not worth the extra complication. ] > https://lore.kernel.org/lkml/20210126171141.122639-1-paul.gortmaker@windriver.com/ > > [v2: push code down from cpu subsys to core bitmap code as per > Yury's comments. Change "last" to simply be "N" as per PeterZ.] > https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/ > > [v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/ > > Cc: Li Zefan > Cc: Ingo Molnar > Cc: Yury Norov > Cc: Thomas Gleixner > Cc: Josh Triplett > Cc: Peter Zijlstra > Cc: "Paul E. McKenney" > Cc: Frederic Weisbecker > Cc: Rasmus Villemoes > Cc: Andy Shevchenko > > > > Paul Gortmaker (8): > lib: test_bitmap: clearly separate ERANGE from EINVAL tests. > lib: test_bitmap: add tests to trigger ERANGE case. > lib: test_bitmap: add more start-end:offset/len tests > lib: bitmap: fold nbits into region struct > lib: bitmap: move ERANGE check from set_region to check_region > lib: bitmap: support "N" as an alias for size of bitmap > lib: test_bitmap: add tests for "N" alias > rcu: deprecate "all" option to rcu_nocbs= > > .../admin-guide/kernel-parameters.rst | 7 +++ > .../admin-guide/kernel-parameters.txt | 4 +- > kernel/rcu/tree_plugin.h | 6 +-- > lib/bitmap.c | 49 +++++++++++-------- > lib/test_bitmap.c | 46 ++++++++++++++--- > 5 files changed, 79 insertions(+), 33 deletions(-) > > -- > 2.30.0 >