From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: Xen 4.2 Release Plan / TODO Date: Mon, 19 Mar 2012 11:33:02 +0000 Message-ID: <1332156782.9223.48.camel@zakaz.uk.xensource.com> References: <1332154645.9223.35.camel@zakaz.uk.xensource.com> <4F6725BB0200007800079400@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F6725BB0200007800079400@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: xen-devel List-Id: xen-devel@lists.xenproject.org On Mon, 2012-03-19 at 11:25 +0000, Jan Beulich wrote: > >>> On 19.03.12 at 11:57, Ian Campbell wrote: > > * file:// backend performance. qemu-xen-tradition's qdisk is quite > > slow & blktap2 not available in upstream kernels. Need to > > consider our options: > > * qemu-xen's qdisk is thought to be well performing but > > qemu-xen is not yet the default. Complexity arising from > > splitting qemu-for-qdisk out from qemu-for-dm and > > running N qemu's. > > * potentially fully userspace blktap could be ready for > > 4.2 > > * use /dev/loop+blkback. This requires loop driver AIO and > > O_DIRECT patches which are not (AFAIK) yet upstream. > > I meant to ask already when this was first mentioned: What's the > reason for this requirement? Didn't we have blkback over loop running > fine for years? Or is this just a performance consideration (in which > case "requires" might be too strong a term)? My understanding (which could well be totally bogus) was that the use of /dev/loop in this way was unsafe since pages were only committed to the dom0 page cache and not to the actual platter when success was reported to the guest. I think that is why many people used tap:aio: instead of file: (personally I use phy: almost exclusively so I could be talking rubbish). Unless there are some loop patches in the classic-Xen patchset? I don't think there are though. I don't know so much about the performance aspect. Stefano might be able to comment. Ian. > > Jan > > > * Leverage XCP's blktap2 DKMS work. > > * Other ideas? > >