From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Chaining sg lists for big I/O commands: Question Date: Wed, 9 May 2007 09:22:08 -0400 (EDT) Message-ID: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: Sender: linux-raid-owner@vger.kernel.org To: axboe@suse.de Cc: linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Alan Piszcz List-Id: linux-raid.ids http://kerneltrap.org/node/8176 I am a mdadm/disk/hard drive fanatic, I was curious: > On i386, we can at most fit 256 scatterlist elements into a page, > and on x86-64 we are stuck with 128. So that puts us somewhere > between 512kb and 1024kb for a single IO. How come 32bit is 256 and 64 is only 128? I am sure it is something very fundamental/simple but I was curious, I would think x86_64 would fit/support more scatterlists in a page. Also, when this patch is implemented for x86_64 and if merged into mainline, what does this mean for performance? I have an mdadm raid5 of 10 raptors and get 434MB/s write and 622MB/s read, would I see an increase in performance with this patch? Justin.