linux-kernel - Re: [PATCH] arm64: Demote boot and shutdown messages to pr

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Date:   Wed, 1 May 2019 11:47:33 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, rmk+kernel@...linux.org.uk,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Julien Thierry <julien.thierry@....com>,
        Suzuki K Poulose <Suzuki.Poulose@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Rob Herring <robh@...nel.org>,
        Steve Capper <steve.capper@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: Demote boot and shutdown messages to pr_debug

On Tue, Apr 30, 2019 at 03:38:31PM -0700, Florian Fainelli wrote:
> Similar to commits c68b0274fb3cf ("ARM: reduce "Booted secondary
> processor" message to debug level") and 035e787543de7 ("ARM: 8644/1: Reduce "CPU:
> shutdown" message to debug level"), demote the secondary_start_kernel()
> and __cpu_die() messages from info, respectively notice to debug. While
> we are at it, also do this for cpu_psci_cpu_kill() which is redundant
> with __cpu_die().
> 
> This helps improve the amount of possible hotplug cycles by around +50%
> on ARCH_BRCMSTB.

Could you elaborate on why that matters? 

e.g. is this just for testing, or does this matter in some shutdown or
hibernate scenario?

> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  arch/arm64/kernel/psci.c | 2 +-
>  arch/arm64/kernel/smp.c  | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> index 8cdaf25e99cd..a78581046c80 100644
> --- a/arch/arm64/kernel/psci.c
> +++ b/arch/arm64/kernel/psci.c
> @@ -96,7 +96,7 @@ static int cpu_psci_cpu_kill(unsigned int cpu)
>  	for (i = 0; i < 10; i++) {
>  		err = psci_ops.affinity_info(cpu_logical_map(cpu), 0);
>  		if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) {
> -			pr_info("CPU%d killed.\n", cpu);
> +			pr_debug("CPU%d killed.\n", cpu);
>  			return 0;
>  		}
>  
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 824de7038967..71fd2b5a3f0e 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -259,7 +259,7 @@ asmlinkage notrace void secondary_start_kernel(void)
>  	 * the CPU migration code to notice that the CPU is online
>  	 * before we continue.
>  	 */
> -	pr_info("CPU%u: Booted secondary processor 0x%010lx [0x%08x]\n",
> +	pr_debug("CPU%u: Booted secondary processor 0x%010lx [0x%08x]\n",
>  					 cpu, (unsigned long)mpidr,
>  					 read_cpuid_id());

I generally agree that we don't need to be verbose, and demoting these
to debug is fine, but it's a shame that these won't be accessible in
defconfig.

I wonder if we should enable DYNAMIC_DEBUG so that we can turn these on
from the kernel command line, or if we should have something like a
verbose_hotplug option specifically for these messages.

Thanks,
Mark.

>  	update_cpu_boot_status(CPU_BOOT_SUCCESS);
> @@ -348,7 +348,7 @@ void __cpu_die(unsigned int cpu)
>  		pr_crit("CPU%u: cpu didn't die\n", cpu);
>  		return;
>  	}
> -	pr_notice("CPU%u: shutdown\n", cpu);
> +	pr_debug("CPU%u: shutdown\n", cpu);
>  
>  	/*
>  	 * Now that the dying CPU is beyond the point of no return w.r.t.
> -- 
> 2.17.1
>