linux-kernel - Re: [PATCH 41/54] arch/x86: replace cpumask_weight with cpumask_weight

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Date:   Mon, 24 Jan 2022 09:05:05 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Laight <David.Laight@...lab.com>,
        Joe Perches <joe@...ches.com>, Dennis Zhou <dennis@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Nicholas Piggin <npiggin@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Alexey Klimov <aklimov@...hat.com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH 41/54] arch/x86: replace cpumask_weight with
 cpumask_weight_eq where appropriate

On Sun, Jan 23, 2022 at 10:39:12AM -0800, Yury Norov wrote:
> smpboot code in somw places calls cpumask_weight() to compare the weight
> of cpumask with a given number. We can do it more efficiently with
> cpumask_weight_eq() because conditional cpumask_weight may stop traversing
> the cpumask earlier, as soon as condition is met.

Why use a more complicated API for code that has no performance
requirements?

>From where I'm sitting this is a net negative for making the code harder
to read.