From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm Date: Mon, 24 May 2010 14:19:34 -0500 Message-ID: <4BFAD146.9090708@codemonkey.ws> References: <20100519192222.GD61706@ncolin.muc.de> <4BF5A9D2.5080609@codemonkey.ws> <4BF91937.2070801@redhat.com> <4BFA5D07.8030309@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Stefan Hajnoczi , Christian Brunner , Blue Swirl , kvm@vger.kernel.org, qemu-devel@nongnu.org, ceph-devel@vger.kernel.org To: Avi Kivity Return-path: In-Reply-To: <4BFA5D07.8030309@redhat.com> Sender: ceph-devel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/24/2010 06:03 AM, Avi Kivity wrote: > On 05/24/2010 11:27 AM, Stefan Hajnoczi wrote: >> On Sun, May 23, 2010 at 1:01 PM, Avi Kivity wrote: >>> On 05/21/2010 12:29 AM, Anthony Liguori wrote: >>>> I'd be more interested in enabling people to build these types of >>>> storage >>>> systems without touching qemu. >>>> >>>> Both sheepdog and ceph ultimately transmit I/O over a socket to a >>>> central >>>> daemon, right? >>> That incurs an extra copy. >> Besides a shared memory approach, I wonder if the splice() family of >> syscalls could be used to send/receive data through a storage daemon >> without the daemon looking at or copying the data? > > Excellent idea. splice() eventually requires a copy. You cannot splice() to linux-aio so you'd have to splice() to a temporary buffer and then call into linux-aio. With shared memory, you can avoid ever bringing the data into memory via O_DIRECT and linux-aio. Regards, Anthony Liguori