linux-kernel - Re: [Patch v2 2/2] x86/tsc: use logical_packages as a better estimation of socket numbers

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Date:   Tue, 27 Jun 2023 13:14:34 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "Paul E . McKenney" <paulmck@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, rui.zhang@...el.com,
        tim.c.chen@...el.com
Subject: Re: [Patch v2 2/2] x86/tsc: use logical_packages as a better
 estimation of socket numbers

On Sun, Jun 25 2023 at 22:51, Feng Tang wrote:
> From debug, the reason of the hung/stall is detect_extended_topology_early()
> is called by cpu hotplug after boot, where there is "maxcpus=XXX" setting,
> (#echo 1 > /sys/devices/system/cpu/cpuX/online).
>
> It could be fixed with below patch:
> ----------------------------------------------------------------
> diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
> index 828c1f7edac1..1ff73c8c4972 100644
> --- a/arch/x86/kernel/cpu/topology.c
> +++ b/arch/x86/kernel/cpu/topology.c
> @@ -29,7 +29,7 @@ unsigned int __max_die_per_package __read_mostly = 1;
>  EXPORT_SYMBOL(__max_die_per_package);
>  
>  #ifdef CONFIG_SMP
> -unsigned int apic_to_pkg_shift __ro_after_init;
> +unsigned int apic_to_pkg_shift;

Bah, yes. I missed the early_init() call from init_intel(). I hate that
code with a passion.