From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?utf-8?Q?Am=C3=A9rico?= Wang Subject: Re: [PATCH 2/3]fs/inode: iunique() Optimize Performance Date: Wed, 25 Nov 2009 22:45:39 +0800 Message-ID: <20091125144539.GA3520@hack> References: <200911252212166092236@gmail.com> <20091125141727.GI9482@parisc-linux.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Liuweni , linux-kernel , viro , akpm , jack , npiggin , linux-fsdevel , strongzgy , xgr178 , Liu Hui To: Matthew Wilcox Return-path: Received: from fg-out-1718.google.com ([72.14.220.154]:43068 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750883AbZKYOo4 (ORCPT ); Wed, 25 Nov 2009 09:44:56 -0500 Content-Disposition: inline In-Reply-To: <20091125141727.GI9482@parisc-linux.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Nov 25, 2009 at 07:17:28AM -0700, Matthew Wilcox wrote: >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. If a compiler can't do this nowadays, I'd consider it's a bug. -- Live like a child, think like the god.