From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH v2] virtio-blk physical block size Date: Mon, 4 Jan 2010 13:38:51 +1030 Message-ID: <201001041338.52621.rusty@rustcorp.com.au> References: <1262018363-15871-1-git-send-email-avi@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Cc: virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, qemu-devel@nongnu.org To: Avi Kivity Return-path: Received: from ozlabs.org ([203.10.76.45]:50809 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751691Ab0ADD7t (ORCPT ); Sun, 3 Jan 2010 22:59:49 -0500 In-Reply-To: <1262018363-15871-1-git-send-email-avi@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, 29 Dec 2009 03:09:23 am Avi Kivity wrote: > This patch adds a physical block size attribute to virtio disks, > corresponding to /sys/devices/.../physical_block_size. It is defined as > the request alignment which will not trigger RMW cycles. This can be > important for modern disks which use 4K physical sectors (though they > still support 512 logical sectors), and for file-backed disk images (which > have both the underlying filesystem block size and their own allocation > granularity to consider). > > Installers use this to align partitions to physical block boundaries. > > Note the spec already defined blk_size as the performance rather than > minimum alignment. However the driver interpreted this as the logical > block size, so I updated the spec to match the driver assuming the driver > predates the spec and that this is an error. I thought this was what I was doing, but I have shown over and over that I have no idea about block devices. Our current driver treats BLK_SIZE as the logical and physical size (see blk_queue_logical_block_size). I have no idea what "logical" vs. "physical" actually means. Anyone? Most importantly, is it some Linux-internal difference or a real I/O-visible distinction? Rusty.