From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay1.corp.sgi.com [137.38.102.111]) by oss.sgi.com (Postfix) with ESMTP id 14EBA7F50 for ; Wed, 13 Nov 2013 12:56:47 -0600 (CST) Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by relay1.corp.sgi.com (Postfix) with ESMTP id D98E28F8035 for ; Wed, 13 Nov 2013 10:56:46 -0800 (PST) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) by cuda.sgi.com with ESMTP id W17C6nybZ2lAJYoC (version=TLSv1 cipher=AES256-SHA bits=256 verify=NO) for ; Wed, 13 Nov 2013 10:56:46 -0800 (PST) Date: Wed, 13 Nov 2013 10:56:45 -0800 From: Christoph Hellwig Subject: Re: [PATCH RFC] xfs: set block device logical sector size on xfs_buftarg Message-ID: <20131113185645.GA20869@infradead.org> References: <5283C41D.7070503@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <5283C41D.7070503@redhat.com> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Eric Sandeen Cc: xfs-oss On Wed, Nov 13, 2013 at 12:25:33PM -0600, Eric Sandeen wrote: > Pure RFC; this might be crazy. Here's the problem I'm trying to solve: > > Today, mkfs.xfs will select a 4k sector size for a 4k physical / 512 logical > drive. (that change was done by me). The thought was that it'd be an > efficiency gain to not make the drive do the (possible) RMW cycles on > 512-byte log IO, primarily. > > However, now this restricts all DIO to 4k alignment, not the otherwise- > possible 512. > > This came up when qemu-kvm, in cache=none mode, tries to boot off an > image hosted on such a filesystem, and its bios wants to do a 512 byte > direct IO read off the disk - it fails. > > But I'm wondering - the buftarg's bt_sshift and bt_smask are only used > in a few places. No need to mess with kernel code IFF we want to change that, just keep the sector size at 512 bytes and set a log stripe unit at mkfs time. I have to admit that I'm not really sure if that's what we really want, through. A drive that has a larger physical block size will need read-modify-write cycles internally, which we try to avoid. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs