linux-kernel - Re: [patch 05/37] x86/topology: Remove CPU0 hotplug option

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Message-ID: <b487a394-0a70-4ec9-ac43-0e8fb14ad110@paulmck-laptop>
Date:   Wed, 21 Jun 2023 09:50:53 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        David Woodhouse <dwmw@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Usama Arif <usama.arif@...edance.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        linux-csky@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Sabin Rapan <sabrapan@...zon.com>
Subject: Re: [patch 05/37] x86/topology: Remove CPU0 hotplug option

On Sat, Apr 15, 2023 at 01:44:21AM +0200, Thomas Gleixner wrote:
> This was introduced together with commit e1c467e69040 ("x86, hotplug: Wake
> up CPU0 via NMI instead of INIT, SIPI, SIPI") to eventually support
> physical hotplug of CPU0:
> 
>  "We'll change this code in the future to wake up hard offlined CPU0 if
>   real platform and request are available."
> 
> 11 years later this has not happened and physical hotplug is not officially
> supported. Remove the cruft.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |   14 ---
>  Documentation/core-api/cpu_hotplug.rst          |   13 ---
>  arch/x86/Kconfig                                |   43 ----------
>  arch/x86/include/asm/cpu.h                      |    3 
>  arch/x86/kernel/topology.c                      |   98 ------------------------
>  arch/x86/power/cpu.c                            |   37 ---------
>  6 files changed, 6 insertions(+), 202 deletions(-)

[ . . . ]

> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2294,49 +2294,6 @@ config HOTPLUG_CPU
>  	def_bool y
>  	depends on SMP
>  
> -config BOOTPARAM_HOTPLUG_CPU0

Removing this requires also removing its use in rcutorture.

I have therefore queued the commit below in -rcu, but please feel
free to take it along with the BOOTPARAM_HOTPLUG_CPU0-removal patch.
Just please let me know if you do.

(Yes, I finally got back to testing -next.  Why do you ask?)

							Thanx, Paul

------------------------------------------------------------------------

commit 95588de780c0e81004b72526aa3e3ef5ce054719
Author: Paul E. McKenney <paulmck@...nel.org>
Date:   Wed Jun 21 09:44:52 2023 -0700

    rcutorture: Remove obsolete BOOTPARAM_HOTPLUG_CPU0 Kconfig option
    
    Now that the BOOTPARAM_HOTPLUG_CPU0 Kconfig option is in the process of
    being removed, it is time to remove rcutorture's use of it.
    
    Link: https://lore.kernel.org/lkml/20230414232309.510911744@linutronix.de/
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
    Cc: Thomas Gleixner <tglx@...utronix.de>
    Cc: <x86@...nel.org>

diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE01 b/tools/testing/selftests/rcutorture/configs/rcu/TREE01
index 04831ef1f9b5..8ae41d5f81a3 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE01
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE01
@@ -15,4 +15,3 @@ CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
-CONFIG_BOOTPARAM_HOTPLUG_CPU0=y