linux-kernel - Re: disabled APICs being counted as processors ?

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Message-ID: <CAE9FiQVUKZ2RsQ_BkePfmpXq+Ty3kj+k7h675fHy8Zm1Za=1Zw@mail.gmail.com>
Date:	Sun, 26 Jan 2014 00:51:23 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Dave Jones <davej@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: disabled APICs being counted as processors ?

On Sun, Jan 26, 2014 at 12:36 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> No, this message is printed in prefill_possible_map() which
> _generates_ cpu_possible_map, so '8' is the number of bits in
> cpu_possible_map.
>
> So the problem is that the counting of disabled but hotpluggable CPUs
> is over-eager. Since I haven't actually seen _true_ hotplug CPU
> hardware yet, I'd argue we do the change below - allocating space for
> never-present CPUs is stupid. If there's true hot-plug CPUs around
> that could come online after we've booted, then we want to know about
> them explicitly.
>
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index a32da80..75a351a 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1223,10 +1223,7 @@ __init void prefill_possible_map(void)
>         i = setup_max_cpus ?: 1;
>         if (setup_possible_cpus == -1) {
>                 possible = num_processors;
> -#ifdef CONFIG_HOTPLUG_CPU
> -               if (setup_max_cpus)
> -                       possible += disabled_cpus;
> -#else
> +#ifndef CONFIG_HOTPLUG_CPU
>                 if (possible > i)
>                         possible = i;
>  #endif

Agreed.

Most happens when one BIOS support different configuration.

Like system support 10 cores cpu and 15 cores cpus or system could be
configured with 4 sockets or 8 sockets

Thanks

Yinghai
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