linux-kernel - Re: [PATCH] parisc: simplify smp_prepare_boot

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Date:   Fri, 20 Oct 2023 15:50:41 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
CC:     Helge Deller <deller@....de>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        <linux-kernel@...r.kernel.org>, James Morse <james.morse@....com>,
        Salil Mehta <salil.mehta@...wei.com>,
        <linux-parisc@...r.kernel.org>
Subject: Re: [PATCH] parisc: simplify smp_prepare_boot_cpu()

On Fri, 20 Oct 2023 15:45:30 +0100
"Russell King (Oracle)" <rmk+kernel@...linux.org.uk> wrote:

> smp_prepare_boot_cpu() reads the cpuid of the first CPU, printing a
> message to state which processor booted, and setting it online and
> present.
> 
> This cpuid is retrieved from per_cpu(cpu_data, 0).cpuid, which is
> initialised in arch/parisc/kernel/processor.c:processor_probe() thusly:
> 
> 	p = &per_cpu(cpu_data, cpuid);
> ...
> 	p->cpuid = cpuid;	/* save CPU id */
> 
> Consequently, the cpuid retrieved seems to be guaranteed to also be
> zero, meaning that the message printed in this boils down to:
> 
> 	pr_info("SMP: bootstrap CPU ID is 0\n");
> 
> Moreover, since kernel/cpu.c::boot_cpu_init() already sets CPU 0 to
> be present and online, there is no need to do this again in
> smp_prepare_boot_cpu().
> 
> Remove this code, and simplify the printk().
> 
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

LGTM, but trivial comment inline.

> ---
>  arch/parisc/kernel/smp.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c
> index 2019c1f04bd0..989efc8c67a5 100644
> --- a/arch/parisc/kernel/smp.c
> +++ b/arch/parisc/kernel/smp.c
> @@ -404,13 +404,8 @@ static int smp_boot_one_cpu(int cpuid, struct task_struct *idle)
>  
>  void __init smp_prepare_boot_cpu(void)
>  {
> -	int bootstrap_processor = per_cpu(cpu_data, 0).cpuid;
> -
>  	/* Setup BSP mappings */

Given it's not doing any such thing, I think you should also drop the comment.

> -	printk(KERN_INFO "SMP: bootstrap CPU ID is %d\n", bootstrap_processor);
> -
> -	set_cpu_online(bootstrap_processor, true);
> -	set_cpu_present(bootstrap_processor, true);
> +	pr_info("SMP: bootstrap CPU ID is 0\n");
>  }
>  
>