linux-kernel - Re: [PATCH v2 0/5] cpumask: cleanup nr_cpu_ids vs nr_cpumask

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Message-ID: <YxdauBT3OPW2mXVz@yury-laptop>
Date:   Tue, 6 Sep 2022 07:35:36 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Sander Vanheule <sander@...nheule.net>,
        Alexey Klimov <klimov.linux@...il.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH v2 0/5] cpumask: cleanup nr_cpu_ids vs nr_cpumask_bits
 mess

On Tue, Sep 06, 2022 at 10:55:20AM +0200, Peter Zijlstra wrote:
> On Mon, Sep 05, 2022 at 04:08:15PM -0700, Yury Norov wrote:
> > cpumask subsystem uses nr_cpu_ids and nr_cpumask_bits interchangeably
> > despite that the variables have different meaning and purpose. It makes
> > some cpumask functions broken.
> > 
> > This series cleans that mess and adds new config FORCE_NR_CPUS that
> > allows to optimize cpumask subsystem if the number of CPUs is known
> > at compile-time.
> 
> Who will use this? Distro's can't,

Raspberry PI can. Smartphone vendors can, and probably should. Ditto
for vehicles and all embedded applications.

> which means 99% of people will not
> use this ever. Is it worth it?

I will definitely enable it for myself. Actually anyone who set NR_CPUS
to a non-default value, may also be interested in FORCE_NR_CPUS.