linux-kernel - Re: [PATCH v2 1/2] init/Kconfig: Fix CPU number in LOG_CPU_MAX_BUF

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Message-ID: <d7cad0f8-5831-7730-42d5-fa6d8c46edbb@molgen.mpg.de>
Date:   Fri, 30 Oct 2020 17:00:18 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     "Luis R . Rodriguez" <mcgrof@...e.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] init/Kconfig: Fix CPU number in
 LOG_CPU_MAX_BUF_SHIFT description

Dear Petr,


Am 11.08.20 um 11:29 schrieb Paul Menzel:
> Currently, LOG_BUF_SHIFT defaults to 17, which is 2 ^ 17 bytes = 128 KB,
> and LOG_CPU_MAX_BUF_SHIFT defaults to 12, which is 2 ^ 12 bytes = 4 KB.
> 
> Half of 128 KB is 64 KB, so more than 16 CPUs are required for the value
> to be used, as then the sum of contributions is greater than 64 KB for
> the first time. My guess is, that the description was written with the
> configuration values used in the SUSE in mind.
> 
> Fixes: 23b2899f7f ("printk: allow increasing the ring buffer depending on the number of CPUs")
> Cc: Luis R. Rodriguez <mcgrof@...e.com>
> Cc: linux-kernel@...r.kernel.org
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> Signed-off-by: Paul Menzel <pmenzel@...gen.mpg.de>
> ---
> v2: Add Reviewed-by tag
> 
>   init/Kconfig | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index d6a0b31b13dc..9dc607e3806f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -718,7 +718,7 @@ config LOG_CPU_MAX_BUF_SHIFT
>   	  with more CPUs. Therefore this value is used only when the sum of
>   	  contributions is greater than the half of the default kernel ring
>   	  buffer as defined by LOG_BUF_SHIFT. The default values are set
> -	  so that more than 64 CPUs are needed to trigger the allocation.
> +	  so that more than 16 CPUs are needed to trigger the allocation.
>   
>   	  Also this option is ignored when "log_buf_len" kernel parameter is
>   	  used as it forces an exact (power of two) size of the ring buffer.

Could you please apply this trivial patch from the two patches already, 
so I do not have to resend it?


Kind regards,

Paul