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

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Message-ID: <20201102134042.GH20201@alley>
Date:   Mon, 2 Nov 2020 14:40:42 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "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

On Fri 2020-10-30 17:00:18, Paul Menzel wrote:
> 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?

The patch is committed in printk/linux.git, branch for-5.10-trivial.

I am not going to create pull request just for this trivial fix.
I will push it for-5.10 only together with eventual more urgent fix.
It is very likely that it will have to wait for 5.11.

Best Regards,
Petr