From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [Xen-devel] Xen blktap driver for Ceph RBD : Anybody wants to test ? :p Date: Mon, 5 Aug 2013 15:04:47 +0100 Message-ID: <51FFB0FF.7070607@eu.citrix.com> References: <20130419064524.GQ11427@reaktio.net> <6035A0D088A63A46850C3988ED045A4B62D9DA64@BITCOM1.int.sbss.com.au> <6035A0D088A63A46850C3988ED045A4B62E7E7E4@BITCOM1.int.sbss.com.au> <20130805111213.GM2924@reaktio.net> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:11111 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753213Ab3HEOEz (ORCPT ); Mon, 5 Aug 2013 10:04:55 -0400 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Sylvain Munaut Cc: =?ISO-8859-1?Q?Pasi_K=E4rkk=E4inen?= , "ceph-devel@vger.kernel.org" , James Harper , "xen-devel@lists.xen.org" , Stefano Stabellini , Roger Pau Monne , Wei Liu 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? > > >> 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