linux-kernel - Re: seq_put_decimal

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Date:	Mon, 26 Mar 2012 10:01:30 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Ulrich Drepper <drepper@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: seq_put_decimal_* optimization

(2012/03/24 21:52), Ulrich Drepper wrote:

> If we want to squeeze out the last drop of slack from the /proc text
> generation, shouldn't we then avoid code like
> 
> +       seq_put_decimal_ull(m, ' ', 0);
> 
> which is worse than what was there before? I realize that the code
> actually becomes more readable like this.  So how about automatically
> optimizing the code by adding something like the following to
> seq_file.h:
> 
> #define seq_put_decimal_ull(m, delimiter, num) \
>   (__builtin_constant_p(num) && \
>    __builtin_constant_p(delimiter) && (delimiter) == ' ' \
>    ? seq_write(m, " " #num, sizeof(" " #num) - 1) \
>    : seq_put_decimal_ull(m, delimiter, num))
> 
> Completely untested and it is a minimal change.  It could be written
> using an inline function and probably made more general that way
> (e.g., handle more delimiters).  But this code should handle the case
> that exist today and lead to a (very small) improvement without any
> real costs to maintenance.
> 

Could you wait a while ?

I'm now considering to add a binary interface /proc/stat.bin and
I would like to use seq_put_decimal_ull() as..
==
int seq_put_decimal_ull(struct seq_file *m, int delimiter, unsigned long long num)
{
	if (m->binstream_format)
		return seq_binstream_attend(num, sizeof(num));
	.....
}
==
Then, we can maintain /proc/stat and /proc/stat.bin in one function
fs/proc/stat.c::show_stat().
Maybe good for applications like top and sa..

Thanks,
-Kame
















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