linux-kernel - Re: [PATCH v4 0/8] support for bitmap (and hence CPU) list "N" abbreviation

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Message-ID: <20210210175751.GH2743@paulmck-ThinkPad-P72>
Date:   Wed, 10 Feb 2021 09:57:51 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
        Ingo Molnar <mingo@...nel.org>,
        Yury Norov <yury.norov@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Triplett <josh@...htriplett.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v4 0/8] support for bitmap (and hence CPU) list "N"
 abbreviation

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???".

Besides, why would someone interpret "N" as "number of CPUs" when doing
that almost always gets you an invalid CPU number?

							Thanx, Paul