linux-kernel - Re: [PATCH] Documentation/admin-guide: kernel-parameters: Update nohlt section

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Message-ID: <62dc4371-d971-9164-1c1d-8923877b5e31@infradead.org>
Date:   Mon, 8 Feb 2021 16:55:03 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org, corbet@....net
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH] Documentation/admin-guide: kernel-parameters: Update
 nohlt section

On 2/8/21 4:30 PM, Florian Fainelli wrote:
> Update the documentation regarding "nohlt" and indicate that it is not
> only for bugs, but can be useful to disable the architecture specific
> sleep instructions. ARM, ARM64, SuperH and Microblaze all use
> CONFIG_GENERIC_IDLE_POLL_SETUP which takes care of honoring the
> "hlt"/"nohlt" parameters.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index a10b545c2070..83c37e23e1e2 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3266,9 +3266,14 @@
>  			parameter, xsave area per process might occupy more
>  			memory on xsaves enabled systems.
>  
> -	nohlt		[BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
> -			wfi(ARM) instruction doesn't work correctly and not to
> -			use it. This is also useful when using JTAG debugger.
> +	nohlt		[ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
> +			in do_idle() and not use the arch_cpu_idle()
> +			implementation, requires CONFIG_GENERIC_IDLE_POLL_SETUP

Sounds good... but above, I would prefer s/,/;/

> +			to be effective. This is useful on platforms where the
> +			sleep(SH) or wfi(ARM,ARM64) instructions do not work
> +			correctly or when doing power measurements to evalute
> +			the impact of the sleep instructions. This is also
> +			useful when using JTAG debugger.
>  
>  	no_file_caps	Tells the kernel not to honor file capabilities.  The
>  			only way then for a file to be executed with privilege
> 

Acked-by: Randy Dunlap <rdunlap@...radead.org>

thanks.

-- 
~Randy