linux-kernel - Re: [PATCH 0/4] printk_index: Fix false positives

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Date: Wed, 28 Feb 2024 19:41:26 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Chris Down <chris@...isdown.name>, Petr Mladek <pmladek@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jessica Yu <jeyu@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jason Baron <jbaron@...mai.com>, Jim Cromie <jim.cromie@...il.com>,
	Ilya Dryomov <idryomov@...il.com>, Xiubo Li <xiubli@...hat.com>,
	Jeff Layton <jlayton@...nel.org>, linux-kernel@...r.kernel.org,
	ceph-devel@...r.kernel.org
Subject: Re: [PATCH 0/4] printk_index: Fix false positives

On Wed, Feb 28, 2024 at 03:00:01PM +0100, Geert Uytterhoeven wrote:
> 	Hi all,
> 
> When printk-indexing is enabled, each printk() invocation emits a
> pi_entry structure, containing the format string and other information
> related to its location in the kernel sources.  This is even true when
> the printk() is protected by an always-false check, as is typically the
> case for debug messages: while the actual code to print the message is
> optimized out by the compiler, the pi_entry structure is still emitted.
> Hence when debugging is disabled, this leads to the inclusion in the
> index of lots of printk formats that cannot be emitted by the current
> kernel.
> 
> This series fixes that for the common debug helpers under include/.
> It reduces the size of an arm64 defconfig kernel with
> CONFIG_PRINTK_INDEX=y by ca. 1.5 MiB, or 28% of the overhead of
> enabling CONFIG_PRINTK_INDEX=y.
> 
> Notes:
>   - netdev_(v)dbg() and netif_(v)dbg() are not affected, as
>     net{dev,if}_printk() do not implement printk-indexing, except
>     for the single global internal instance of __netdev_printk().
>   - This series fixes only debug code in global header files under
>     include/.  There are more cases to fix in subsystem-specific header
>     files and in sources files.


The whole series makes a lot of sense and gives a good examples for above
mentioned subsystem specific code on how to do it in a better way.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

-- 
With Best Regards,
Andy Shevchenko