linux-kernel - Re: [RFC PATCH] ACPI / processor: Get accurate possible CPU count

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Message-ID: <CAHp75VfGPgbD8gBdvchBn5U8gH93zoHB9ja3KucUuxVNq+_MLg@mail.gmail.com>
Date:   Wed, 14 Mar 2018 19:24:14 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Artem Bityutskiy <dedekind1@...il.com>, ming.lei@...hat.com
Subject: Re: [RFC PATCH] ACPI / processor: Get accurate possible CPU count

On Wed, Mar 14, 2018 at 12:28 PM, Dou Liyang <douly.fnst@...fujitsu.com> wrote:

> +static void __init acpi_update_possible_map(void)
> +{
> +       unsigned int cpu, nr = 0;
> +

> +       if (nr_cpu_ids <= nr_unique_ids)
> +               return;
> +
> +       for_each_possible_cpu(cpu) {
> +               if (nr >= nr_unique_ids)
> +                       set_cpu_possible(cpu, false);
> +               nr++;
> +       }

IIUC this can be optimized to:

if (nr_unique_ids >= nr_cpu_ids)
    return;

/* Don't yet figure out if it's superfluous */
if (nr_unique_ids >= cpumask_last(cpu_possible_mask))
    return;

for_each_cpu_wrap(cpu, cpu_possible_mask, nr_unique_ids)
    set_cpu_possible(cpu, false);

> +       nr_cpu_ids = nr_unique_ids;
> +       pr_info("Allowing %d possible CPUs\n", nr_cpu_ids);
> +}

-- 
With Best Regards,
Andy Shevchenko