linux-kernel - Re: [patch v3 13/36] x86/smpboot: Remove cpu_callin

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Message-ID: <20230509104915.GX83892@hirez.programming.kicks-ass.net>
Date:   Tue, 9 May 2023 12:49:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        David Woodhouse <dwmw2@...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>,
        Paul McKenney <paulmck@...nel.org>,
        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>,
        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>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Subject: Re: [patch v3 13/36] x86/smpboot: Remove cpu_callin_mask

On Mon, May 08, 2023 at 09:43:47PM +0200, Thomas Gleixner wrote:

> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c

> @@ -167,21 +166,16 @@ static inline void smpboot_restore_warm_
>   */
>  static void smp_callin(void)
>  {
> -	int cpuid;
> +	int cpuid = smp_processor_id();
>  
>  	/*
>  	 * If waken up by an INIT in an 82489DX configuration
> -	 * cpu_callout_mask guarantees we don't get here before
> -	 * an INIT_deassert IPI reaches our local APIC, so it is
> -	 * now safe to touch our local APIC.
> -	 */
> -	cpuid = smp_processor_id();
> -
> -	/*
> -	 * the boot CPU has finished the init stage and is spinning
> -	 * on callin_map until we finish. We are free to set up this
> -	 * CPU, first the APIC. (this is probably redundant on most
> -	 * boards)
> +	 * cpu_callout_mask guarantees we don't get here before an
> +	 * INIT_deassert IPI reaches our local APIC, so it is now safe to
> +	 * touch our local APIC.
> +	 *
> +	 * Set up this CPU, first the APIC, which is probably redundant on
> +	 * most boards.
>  	 */
>  	apic_ap_setup();
>  
> @@ -192,7 +186,7 @@ static void smp_callin(void)
>  	 * The topology information must be up to date before
>  	 * calibrate_delay() and notify_cpu_starting().
>  	 */
> -	set_cpu_sibling_map(raw_smp_processor_id());
> +	set_cpu_sibling_map(cpuid);
>  
>  	ap_init_aperfmperf();
>  
> @@ -205,11 +199,6 @@ static void smp_callin(void)
>  	 * state (CPUHP_ONLINE in the case of serial bringup).
>  	 */
>  	notify_cpu_starting(cpuid);
> -
> -	/*
> -	 * Allow the master to continue.
> -	 */
> -	cpumask_set_cpu(cpuid, cpu_callin_mask);
>  }
>  
>  static void ap_calibrate_delay(void)
> @@ -268,11 +257,6 @@ static void notrace start_secondary(void
>  	rcu_cpu_starting(raw_smp_processor_id());
>  	x86_cpuinit.early_percpu_clock_init();
>  
> -	/*
> -	 * Sync point with wait_cpu_callin(). The AP doesn't wait here
> -	 * but just sets the bit to let the controlling CPU (BSP) know that
> -	 * it's got this far.
> -	 */
>  	smp_callin();
>  
>  	/* Otherwise gcc will move up smp_processor_id() before cpu_init() */

Good riddance to that mask; however is smp_callin() still an appropriate
name for that function?

Would smp_starting() -- seeing how this kicks of CPU_STARTING not be a
better name?