From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [Xen-devel] Xen blktap driver for Ceph RBD : Anybody wants to test ? :p Date: Mon, 5 Aug 2013 16:18:14 +0100 Message-ID: <20130805151814.GG27858@zion.uk.xensource.com> References: <20130419064524.GQ11427@reaktio.net> <6035A0D088A63A46850C3988ED045A4B62D9DA64@BITCOM1.int.sbss.com.au> <6035A0D088A63A46850C3988ED045A4B62E7E7E4@BITCOM1.int.sbss.com.au> <20130805111213.GM2924@reaktio.net> <51FFB0FF.7070607@eu.citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:42824 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752271Ab3HEPSP (ORCPT ); Mon, 5 Aug 2013 11:18:15 -0400 Content-Disposition: inline In-Reply-To: <51FFB0FF.7070607@eu.citrix.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: George Dunlap Cc: Sylvain Munaut , Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?= , "ceph-devel@vger.kernel.org" , James Harper , "xen-devel@lists.xen.org" , Stefano Stabellini , Roger Pau Monne , Wei Liu On Mon, Aug 05, 2013 at 03:04:47PM +0100, George Dunlap wrote: > On 05/08/13 14:55, Sylvain Munaut wrote: > >Hi George, > > > > > >>Yes; qemu knows how to be a Xen PV block back-end. > >Very interesting. Is there documentation about this somewhere ? > >I had a look some time ago and it was really not very clear. > > > >Things like what Xen version support this. And with which features ( > >indirect descriptors, persistent grants, discard, flush, ...) and/or > >which limitation. > > I don't think this is documented anywhere; you'll need to ask the > experts. Stefano? Roger? Wei? > These are Linux features not Xen ones AFAICT. In theory they are not bound to specific Xen versions. For the network part I don't think new features depend on any specific hypercall. However for block Roger and Stefano seem to introduce new hypercalls for certain features (I might be wrong though). Wei. > > > > > >>One of the reasons for stopping work on blktap3 (AIUI) was that it > >>should in theory have performance characteristics similar to blktap3, > >And did anyone check the theory currently ? :) > > I say "in theory" because they are using the same basic > architecture: a normal process running in dom0, with no special > kernel support. If there were a performance difference, it would be > something that should (in theory) be able to be optimized. > > I don't think we have comparisons between qdisk (which is what we > call qemu-as-pv-backend in Xen) and blktap3 (and since blktap3 > wasn't finished they wouldn't mean much anyway); but I think qdisk > compares reasonably with blkback. > > -George