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[5.186.115.188]) by smtp.gmail.com with ESMTPSA id hb24sm4089174ejb.16.2021.02.11.03.04.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Feb 2021 03:04:52 -0800 (PST) Subject: Re: [PATCH v4 0/8] support for bitmap (and hence CPU) list "N" abbreviation To: paulmck@kernel.org, Andy Shevchenko Cc: Paul Gortmaker , linux-kernel@vger.kernel.org, Li Zefan , Ingo Molnar , Yury Norov , Thomas Gleixner , Josh Triplett , Peter Zijlstra , Frederic Weisbecker References: <20210209225907.78405-1-paul.gortmaker@windriver.com> <20210210175751.GH2743@paulmck-ThinkPad-P72> From: Rasmus Villemoes Message-ID: Date: Thu, 11 Feb 2021 12:04:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210210175751.GH2743@paulmck-ThinkPad-P72> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/02/2021 18.57, Paul E. McKenney wrote: > On Wed, Feb 10, 2021 at 06:26:54PM +0200, Andy Shevchenko wrote: >> On Tue, Feb 09, 2021 at 05:58:59PM -0500, Paul Gortmaker wrote: >>> 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. >> >> I thought we kinda agreed that N is confusing and L is better. >> N to me is equal to 32 on 32 core system as *number of cores / CPUs*. While L >> sounds better as *last available CPU number*. > > The advantage of "N" is that people will automatically recognize it as > "last thing" or number of things" because "N" has long been used in > both senses. In contrast, someone seeing "0-L" for the first time is > likely to go "What???". Completely agree. The patch that introduces this even updates Documentation/ at the same time, and if people are confused just because they don't RTFM, xkcd#293 applies. So let's please just paint the bikeshed N. (As for case insensitivity, I don't see the point, it just makes documentation and implementation more cumbersome and confusing. Just document and implement _one_ way of doing this.) As for a future syntax for "last 4 cpus", it's common to accept a negative index to mean count from the end, so unless we already accept -4 as a shorthand for 0-4 (haven't checked), that could be -4-N. But regardless, I also agree with Paul on this point, that's for a future time when the need arises. Rasmus