linux-kernel - Re: [PATCH] vsprintf: uninline simple

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Message-ID: <ZUKBa0iTH6YBIPS_@alley>
Date:   Wed, 1 Nov 2023 17:48:43 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vsprintf: uninline simple_strntoull(), reorder arguments

On Fri 2023-10-27 17:13:58, Alexey Dobriyan wrote:
> * uninline simple_strntoull(),
>   gcc overinlines and this function is not performance critical
> 
> * reorder arguments, so that appending INT_MAX as 4th argument
>   generates very efficient tail call
> 
> Space savings:
> 
> 	add/remove: 1/0 grow/shrink: 0/3 up/down: 27/-179 (-152)
> 	Function                            old     new   delta
> 	simple_strntoll                       -      27     +27
> 	simple_strtoull                      15      10      -5
> 	simple_strtoll                       41       7     -34
> 	vsscanf                            1930    1790    -140
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>

I am usually quite skeptical about these micro-optimizations. They might
help only on some architectures with some compiler versions. And
they might make it worse for others.

Well, I could imagine that passing constant via the last parameter
might help in most cases. And the new ordering of the parameters
is fine. So let's get it in.

Reviewed-by: Petr Mladek <pmladek@...e.com>

I have just pushed the patch into printk/linux.git, branch for-6.7.

Best Regards,
Petr