From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: LBA starting address alignment from struct request Date: Mon, 8 Dec 2014 08:39:07 +1100 Message-ID: <20141207213907.GO18131@dastard> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org To: Alvin Abitria Return-path: Received: from ipmail06.adl6.internode.on.net ([150.101.137.145]:13882 "EHLO ipmail06.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752005AbaLGVjU (ORCPT ); Sun, 7 Dec 2014 16:39:20 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sun, Dec 07, 2014 at 11:49:41AM +0800, Alvin Abitria wrote: > Hello, > > Currently doing block drivers. I've noticed during my tests that if > my platform are RHEL6.x/CentOS6.x my struct request's starting > LBA/sector is always aligned to 8 (e.g. 0, 8, 0x100, 0x2508, etc.) > which is actually desirable for my designed driver. It seems the > struct requests are always aligned there. > > On the other hand, if I test on some older systems like Oracle 5.6, > the starting LBA for struct requests there seems not to be aligned to > 8 - most cases the LBA is offseted (e.g. 0x2507, 300f, 0x95bd500f, > etc.) > > My block queue settings and even looking from sysfs shows that my > logical block size and physical block size are 512 and 512, > respectively. So I don't think it has something to do with 4kB > sectors. What could be the setting that triggered such behaviour? Partition alignment and filesystem type and configuration will determine if IOs on arbitrary sector alignments are done. Some filesystems will *always* do some amount of arbitrarily sector aligned IO even when using a 4k block size. And if you configure a filesystem to use a 512 byte block size, then you'll almost always get non-aligned IO requests. Hence if your block device can only handle 4k aligned and sized IO then it needs to preset a block device with a 4k sector size. That will result in everything using the block device to issue 4k aligned and sized IOs.... Cheers, Dave. -- Dave Chinner david@fromorbit.com