linux-kernel - Re: [PATCH RFC cpumask] Allow "all", "none", and "last" in cpumask strings

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Message-ID: <CAAH8bW95nyx6PEnPiBPoHMLoduvgU9KO7N=K7mhLORkA+zzhDw@mail.gmail.com>
Date:   Wed, 6 Jan 2021 00:49:46 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     paulmck@...nel.org
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paul.gortmaker@...driver.com, kernel-team@...com
Subject: Re: [PATCH RFC cpumask] Allow "all", "none", and "last" in cpumask strings

On Tue, Jan 5, 2021 at 4:48 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> Hello!
>
> This series allows "all", "none", and "last" to be used in cpumask
> strings.  This allows these strings to be less dependent on the underlying
> system.  For example, currently a string specifying all but the first
> CPU must be "1-7" on an eight-CPU system and "1-15" on a 16-CPU system.
> With this series, the single string "1-last" can be used regardless of the
> number of CPUs (at least assuming that each system has at least one CPU).

'none' may be implemented as an empty string or string with separators only,
but I have nothing against explicit 'none'. See other comments inline.

Thanks,
Yury.

> 1.      Un-inline cpulist_parse for SMP; prepare for ascii helpers,
>         courtesy of Paul Gortmaker.
>
> 2.      Make "all" alias global and not just RCU, courtesy of Paul
>         Gortmaker.
>
> 3.      Add a "none" alias to complement "all", courtesy of Paul
>         Gortmaker.
>
> 4.      Add "last" alias for cpu list specifications, courtesy of Paul
>         Gortmaker.
>
> 5.      Use "all" and "last" in "nohz_full" and "rcu_nocbs".
>
>                                                 Thanx, Paul
>
> ------------------------------------------------------------------------
>
>  Documentation/admin-guide/kernel-parameters.rst            |   20 +
>  Documentation/admin-guide/kernel-parameters.txt            |    4
>  include/linux/cpumask.h                                    |    8
>  kernel/rcu/tree_plugin.h                                   |   13 -
>  lib/cpumask.c                                              |  136 ++++++++++++-
>  tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot |    2
>  tools/testing/selftests/rcutorture/configs/rcu/TREE08.boot |    2
>  7 files changed, 169 insertions(+), 16 deletions(-)