From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38169) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fj00O-0002Jn-BZ for qemu-devel@nongnu.org; Fri, 27 Jul 2018 06:29:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fj00N-0003NH-JD for qemu-devel@nongnu.org; Fri, 27 Jul 2018 06:29:52 -0400 Date: Fri, 27 Jul 2018 12:29:38 +0200 From: Kevin Wolf Message-ID: <20180727102938.GD4355@localhost.localdomain> References: <20180727033402.13513-1-famz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180727033402.13513-1-famz@redhat.com> Subject: Re: [Qemu-devel] [PATCH RFC for-3.0-rc3 0/3] qemu-img: Disable copy offloading by default List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: qemu-devel@nongnu.org, stefanha@redhat.com, Max Reitz , qemu-block@nongnu.org Am 27.07.2018 um 05:33 hat Fam Zheng geschrieben: > Kevin pointed out that both glibc and kernel provides a slow fallback of > copy_file_range which hurts thin provisioning. This is particularly true for > thin LVs, because host_device driver cannot get allocation info from the > volume, and copy_file_range is called on every sectors, making the dst fully > allocated. > > NFS mount points also doesn't support SEEK_DATA well, so the allocation > information is unknown to QEMU. > > That leaves only iscsi:// which seems to do what we want so far, but it is a > smaller use case. > > Add an option to qemu-img convert, "-C", to enable (attempting) copy offloading > explicitly. And mark it incompatible with "-S" and "-c". Reviewed-by: Kevin Wolf Not sure why you made this an RFC only, but I think we absolutely need this. People are used to using 'qemu-img convert' to compact images and this would regress with automatic copy offloading. Do you think we need more discussion? Kevin