From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53796) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fdeNs-00009F-Pj for qemu-devel@nongnu.org; Thu, 12 Jul 2018 12:24:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fdeNr-0006yU-Px for qemu-devel@nongnu.org; Thu, 12 Jul 2018 12:24:00 -0400 Date: Thu, 12 Jul 2018 18:23:51 +0200 From: Kevin Wolf Message-ID: <20180712162351.GG4541@localhost.localdomain> References: <1531400410-27059-1-git-send-email-pl@kamp.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1531400410-27059-1-git-send-email-pl@kamp.de> Subject: Re: [Qemu-devel] [PATCH V6] qemu-img: align result of is_allocated_sectors List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Am 12.07.2018 um 15:00 hat Peter Lieven geschrieben: > We currently don't enforce that the sparse segments we detect during convert are > aligned. This leads to unnecessary and costly read-modify-write cycles either > internally in Qemu or in the background on the storage device as nearly all > modern filesystems or hardware have a 4k alignment internally. > > This patch modifies is_allocated_sectors so that its *pnum result will always > end at an alignment boundary. This way all requests will end at an alignment > boundary. The start of all requests will also be aligned as long as the results > of get_block_status do not lead to an unaligned offset. > > The number of RMW cycles when converting an example image [1] to a raw device that > has 4k sector size is about 4600 4k read requests to perform a total of about 15000 > write requests. With this path the additional 4600 read requests are eliminated while > the number of total write requests stays constant. > > [1] https://cloud-images.ubuntu.com/releases/16.04/release/ubuntu-16.04-server-cloudimg-amd64-disk1.vmdk > > Signed-off-by: Peter Lieven Thanks, applied to the block branch. Kevin