linux-kernel - Re: [PATCH v5 1/3] printk: Fix LOG_CPU_MAX_BUF_SHIFT when BASE

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Date: Thu, 15 Feb 2024 06:36:50 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Yoann Congal <yoann.congal@...le.fr>
Cc: linux-fsdevel@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, x86@...nel.org, 
	André Almeida <andrealmeid@...lia.com>, 
	Borislav Petkov <bp@...en8.de>, Darren Hart <dvhart@...radead.org>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Davidlohr Bueso <dave@...olabs.net>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Jiri Slaby <jirislaby@...nel.org>, 
	John Ogness <john.ogness@...utronix.de>, Josh Triplett <josh@...htriplett.org>, 
	Matthew Wilcox <willy@...radead.org>, Peter Zijlstra <peterz@...radead.org>, 
	Petr Mladek <pmladek@...e.com>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Willem de Bruijn <willemdebruijn.kernel@...il.com>, Vegard Nossum <vegard.nossum@...cle.com>
Subject: Re: [PATCH v5 1/3] printk: Fix LOG_CPU_MAX_BUF_SHIFT when BASE_SMALL
 is enabled

On Tue, Feb 13, 2024 at 4:01 AM Yoann Congal <yoann.congal@...le.fr> wrote:
>
>
>
> Le 11/02/2024 à 00:41, Masahiro Yamada a écrit :
> > On Thu, Feb 8, 2024 at 2:10 AM Yoann Congal <yoann.congal@...lefr> wrote:
> >>
> >> LOG_CPU_MAX_BUF_SHIFT default value depends on BASE_SMALL:
> >>   config LOG_CPU_MAX_BUF_SHIFT
> >>         default 12 if !BASE_SMALL
> >>         default 0 if BASE_SMALL
> >> But, BASE_SMALL is a config of type int and "!BASE_SMALL" is always
> >> evaluated to true whatever is the value of BASE_SMALL.
> >>
> >> This patch fixes this by using the correct conditional operator for int
> >> type : BASE_SMALL != 0.
> >>
> >> Note: This changes CONFIG_LOG_CPU_MAX_BUF_SHIFT=12 to
> >> CONFIG_LOG_CPU_MAX_BUF_SHIFT=0 for BASE_SMALL defconfigs, but that will
> >> not be a big impact due to this code in kernel/printk/printk.c:
> >>   /* by default this will only continue through for large > 64 CPUs */
> >>   if (cpu_extra <= __LOG_BUF_LEN / 2)
> >>           return;
> >> Systems using CONFIG_BASE_SMALL and having 64+ CPUs should be quite
> >> rare.
> >>
> >> John Ogness <john.ogness@...utronix.de> (printk reviewer) wrote:
> >>> For printk this will mean that BASE_SMALL systems were probably
> >>> previously allocating/using the dynamic ringbuffer and now they will
> >>> just continue to use the static ringbuffer. Which is fine and saves
> >>> memory (as it should).
> >>
> >> Petr Mladek <pmladek@...e.com> (printk maintainer) wrote:
> >>> More precisely, it allocated the buffer dynamically when the sum
> >>> of per-CPU-extra space exceeded half of the default static ring
> >>> buffer. This happened for systems with more than 64 CPUs with
> >>> the default config values.
> >>
> >> Signed-off-by: Yoann Congal <yoann.congal@...le.fr>
> >> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> >> Closes: https://lore.kernel.org/all/CAMuHMdWm6u1wX7efZQf=2XUAHascps76YQac6rdnQGhc8nop_Q@mail.gmail.com/
> >> Reported-by: Vegard Nossum <vegard.nossum@...cle.com>
> >> Closes: https://lore.kernel.org/all/f6856be8-54b7-0fa0-1d17-39632bf29ada@oracle.com/
> >> Fixes: 4e244c10eab3 ("kconfig: remove unneeded symbol_empty variable")
> >>
> >
> >
> >
> > All the Reviewed-by tags are dropped every time, annoyingly.
>
> Hi!
>
> Was I supposed to gather these tags from patch version N to patch version N+1?
> In that case, I'm sorry, I did not know that :-/
> Patch 1/3 is exactly the same but patch 2/3 is equivalent but different. Is there a rule written somewhere about when carrying the tags across revision and when not? (I could not find it)


I do not know any written rules either.


In my experience, people carry tags
when changes since the previous version are small.





-- 
Best Regards
Masahiro Yamada