linux-kernel - Re: [PATCH 1/2] bitmap_parse: support 'all' semantics

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Message-ID: <20210421234527.GD194948@windriver.com>
Date:   Wed, 21 Apr 2021 19:45:27 -0400
From:   Paul Gortmaker <paul.gortmaker@...driver.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org,
        rcu@...r.kernel.org, linux-doc@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jonathan Corbet <corbet@....net>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH 1/2] bitmap_parse: support 'all' semantics

[Re: [PATCH 1/2] bitmap_parse: support 'all' semantics] On 21/04/2021 (Wed 11:19) Steven Rostedt wrote:

> On Tue, 20 Apr 2021 20:13:25 -0700
> Yury Norov <yury.norov@...il.com> wrote:
> 
> > @@ -76,6 +76,11 @@ to change, such as less cores in the CPU list, then N and any ranges using N
> >  will also change.  Use the same on a small 4 core system, and "16-N" becomes
> >  "16-3" and now the same boot input will be flagged as invalid (start > end).
> >  
> > +The special case-tolerant group name "all" has a meaning of selecting all CPUs,
> > +such that "isolcpus=all" is the equivalent of "isolcpus=0-N".
> 
> I'm OK with the concept of this patch set, but really? That is a horrible
> example. One should NEVER set isolcpus to all!

It wouldn't have parsed anyways.  The "isolcpus=" would just think "all" was
an unsupported flag and discard it before it ever got to cpu/bitmap
processing.   See 3662daf02350 "sched/isolation: Allow "isolcpus=" to
skip unknown sub-parameters".

The use case example Paul chose (not me; the smart Paul) is better.

Paul.
--

> 
> -- Steve
> 
> 
> > +
> > +The semantics of "N" and "all" is supported on a level of bitmaps and holds for
> > +all users of bitmap_parse().
> >