linux-kernel - Re: [RFC PATCH] seq_file: Use seq_puts when seq

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Message-ID: <20130316175446.GA21522@ZenIV.linux.org.uk>
Date:	Sat, 16 Mar 2013 17:54:47 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Joe Perches <joe@...ches.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] seq_file: Use seq_puts when seq_printf has only a
 format with no args

On Sat, Mar 16, 2013 at 06:50:44AM -0700, Joe Perches wrote:
> Instead of converting the 800 or so uses of seq_printf with
> a constant format (without a % substitution) to seq_puts,
> maybe there's another way to slightly speed up these outputs.
> 
> Taking a similar approach to commit abd84d60eb
> ("tracing: Optimize trace_printk() with one arg to use trace_puts()")
> use the preprocessor to convert seq_printf(seq, "string constant")
> to seq_puts(seq, "string constant")
> 
> By stringifying __VA_ARGS__, we can, at compile time, determine
> the number of args that are being passed to seq_printf() and
> call seq_puts or seq_printf appropriately.
> 
> The actual function definition for seq_printf must now
> be enclosed in parenthesis to avoid further macro expansion.

Joe, would you mind showing me a single real-world case where that
"optimization" would really matter?  Adding a module that would
produce a seq_file in procfs, with contents generated by something like
	for(i = 0; i < 4000; i++)
		seq_printf(m, "a");
and application that would keep reading that file in a loop does not count,
TYVM.  Until then,
NAKed-by: Al Viro <viro@...iv.linux.org.uk>
NAKed-because: GAFL
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