From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matthew Wilcox <matthew@wil.cx>
Subject: Re: [PATCH 2/3]fs/inode: iunique() Optimize Performance
Date: Wed, 25 Nov 2009 07:17:28 -0700
Message-ID: <20091125141727.GI9482@parisc-linux.org>
References: <200911252212166092236@gmail.com>
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Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	viro <viro@zeniv.linux.org.uk>, akpm <akpm@linux-foundation.org>,
	jack <jack@suse.cz>, npiggin <npiggin@suse.de>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	strongzgy <strongzgy@gmail.com>, xgr178 <xgr178@163.com>,
	Liu Hui <onlyflyer@gmail.com>
To: Liuweni <qingshenlwy@gmail.com>
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On Wed, Nov 25, 2009 at 10:12:19PM +0800, Liuweni wrote:
> @@ -605,8 +605,8 @@ static unsigned long hash(struct super_block *sb, unsigned long hashval)
>  {
>  	unsigned long tmp;
>  
> -	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
> -			L1_CACHE_BYTES;
> +	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) >>
> +			L1_CACHE_SHIFT;
>  	tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
>  	return tmp & I_HASHMASK;
>  }

Have you compared the compiler output before/after your change?  I'd be
amazed if GCC isn't able to optimise division-by-a-constant-power-of-two
into shift-by-constant.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."