linux-kernel - Re: [PATCH v4 7/7] kernel.h: drop trace

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Message-ID: <7df7c705c02cae6d609a3bc5f153082cf0658a60@intel.com>
Date: Mon, 05 Jan 2026 20:30:54 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Yury Norov <yury.norov@...il.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Joel Fernandes
 <joelagnelf@...dia.com>, Steven Rostedt <rostedt@...dmis.org>, Andrew
 Morton <akpm@...ux-foundation.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Christophe Leroy <chleroy@...nel.org>, Randy Dunlap
 <rdunlap@...radead.org>, Ingo Molnar <mingo@...nel.org>, Joonas Lahtinen
 <joonas.lahtinen@...ux.intel.com>, David Laight <david.laight@...box.com>,
 Petr Pavlu <petr.pavlu@...e.com>, Andi Shyti <andi.shyti@...nel.org>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, Daniel Gomez <da.gomez@...nel.org>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>,
 linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, linux-modules@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/7] kernel.h: drop trace_printk.h

On Mon, 05 Jan 2026, Yury Norov <yury.norov@...il.com> wrote:
> On Mon, Jan 05, 2026 at 11:29:51AM +0200, Jani Nikula wrote:
>> On Sat, 03 Jan 2026, Yury Norov <yury.norov@...il.com> wrote:
>> > On Sat, Jan 03, 2026 at 02:57:58PM +0200, Andy Shevchenko wrote:
>> >> On Fri, Jan 02, 2026 at 07:50:59PM -0500, Joel Fernandes wrote:
>> >> > On Mon, Dec 29, 2025 at 11:17:48AM -0500, Steven Rostedt wrote:
>> >> 
>> >> ...
>> >> 
>> >> > I use trace_printk() all the time for kernel, particularly RCU development.
>> >> > One of the key usecases I have is dumping traces on panic (with panic on warn
>> >> > and stop tracing on warn enabled). This is extremely useful since I can add
>> >> > custom tracing and dump traces when rare conditions occur. I fixed several
>> >> > bugs with this technique.
>> >> > 
>> >> > I also recommend keeping it convenient to use.
>> >> 
>> >> Okay, you know C, please share your opinion what header is the best to hold the
>> >> trace_printk.h to be included.
>> >
>> > What if we include it on Makefile level, similarly to how W=1 works?
>> >
>> >         make D=1 // trace_printk() is available
>> >         make D=0 // trace_printk() is not available
>> >         make     // trace_printk() is not available
>> >
>> > Where D stands for debugging.
>> >
>> > D=1 may be a default setting if you prefer, but the most important is
>> > that every compilation unit will have an access to debugging without
>> > polluting core headers.
>> 
>> You do realize this means recompiling everything when adding D=1 for
>> debugging?
>
> Yes sir I do.
>
> It would be as simple (or hard) as building another arch:
>
>         make O=../build/linux-arm64
>         make O=../build/linux-x86_64
>         make D=1 W=1 O=../build/linux-x86_64-dev
>
> If you're both developer and CI engineer in your company, you're likely
> already doing something like that. If you're CI-only, there're no
> changes for you. If you're a developer - yeah, you'd have to learn a
> new flag.

Learn a new flag?

What I'm saying is, if you're doing regular builds as a developer, and
*then* realize you need trace_printk(), doing your suggested 'make D=1'
rebuilds *everything*. Not exactly something you want in the middle of
your development flow.

I'd *rather* manually add that #include where needed, and rebuild just
those files. I don't even feel very strongly about the whole thing,
other than the D=1 being the worst suggestion so far in the thread.

BR,
Jani.

>
> The real problem of course is the status inflation. The fact that
> defconfig enables CONFIG_EXPERT and CONFIG_DEBUG_KERNEL implies that
> every random person who is able to do:
>
>         git clone && make && sudo make install
>
> now assumed an expert kernel user and active developer. It is not
> correct, and it leads to bloating kernel with dev-only features.
>
> What we discuss here is a new marker for those real experts and
> developers, I think. (In an hope that it will inflate not very fast.)
>
> Thanks,
> Yury

-- 
Jani Nikula, Intel