linux-kernel - Re: [PATCH] fs/buffer.c: change buffer_busy() to use logical-OR expression

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Message-ID: <20101023172107.GQ19804@ZenIV.linux.org.uk>
Date:	Sat, 23 Oct 2010 18:21:07 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/buffer.c: change buffer_busy() to use logical-OR
 expression

On Sun, Oct 24, 2010 at 02:06:15AM +0900, Namhyung Kim wrote:
> Convert bitwise-OR operator to logical-OR in favor of short-circuit
> evaluation. The end result would be same.

It'll cost _more_.

Think of it:
	v = atomic_read(...)
	w = bh->b_state
	w &= constant
	v |= w
	return v
vs.
	v = atomic_read()
	branch to l if not equal to 0
	w = bh->b_state
	if w & constant is not 0, branch to l
	v = 0
	return v
l:	v = 1
	return v

That short-circuit won't win anything here.
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