WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] request of blkfront may disorder after migration without

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] request of blkfront may disorder after migration without waiting in suspend phase of migration
From: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Date: Wed, 13 Jul 2011 19:03:57 -0700
Cc: alice wan <wanjia19870902@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Delivery-date: Wed, 13 Jul 2011 19:04:53 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <1310548191.634.353.camel@xxxxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <CAKQ7UJnkTREkHw11_C46CTLzXwcgB_ADSGFONCMDKjPU=0nHKw@xxxxxxxxxxxxxx> <20110712182335.GA24828@xxxxxxxxxxxx> <1310548191.634.353.camel@xxxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
On Wed, 2011-07-13 at 05:09 -0400, Ian Campbell wrote: 
> On Tue, 2011-07-12 at 19:23 +0100, Konrad Rzeszutek Wilk wrote:
> > On Sun, Jul 10, 2011 at 12:36:06PM +0800, alice wan wrote:
> > > Hi konrad,
> > > 
> > > I found the mainline linux 3.0-rc6 xen-blkfront driver doesn't implement
> > > suspend func. In my opinion, the blkfront should wait till responses of 
> > > all
> > > the pending requests come back, then domu can be suspended,
> > 
> > I think you mean blkback. It should be the job of blkback to account for
> > all I/Os and make sure they have completed before migrating?
> 
> blkfront has a resume hook which (AIUI) is intended to recover things
> after a migration and this seemingly does not require any work on the
> suspend path (or at least was presumably thought not to when it was
> written...).

>From a pre-copy migration perspective, adding a suspend hook to synch on
pending I/O is not ideal. It's just going to add unsolicited memory
footprint, with fairly arbitrary amounts of additional memory getting
dirtied ('arbitrary' depending on what else is allowed to keep running
in the guest in that state).

I guess that's why post-migration recovery was preferred, and I still
don't see why that's to blame.

Daniel

> Ian.
> 
> > 
> > I did have a patch for the 2.6.32 to deal with this but I never was able
> > to reproduce this. Are you able to reproduce this? Can you give me
> > step by step instructions on how to do it?
> > 
> > > otherwise,  after the migration, vm of target host will request from 
> > > target
> > > host, meanwhile, the blkback of source host maybe do the pending requests
> > > until they's done.
> > > 
> > > if migrate the vm with high io pressure,  the requests of this vm may
> > > disorder.
> > > 
> > > And i saw the gpl windows pv driver, blkfront will change its state and 
> > > wait
> > > for blkback closing, after blkback closing, the pending requests 
> > > definitely
> > > are done.
> > > 
> > > More, i did some test with migration,  while vm was running dd task,  xm
> > > migrate -l .  before it suspend, gdb tapdisk2.  after migration, new vm
> > > started. then quit gdb, the pending request were written back to disk 
> > > after
> > > new requests.
> > > 
> > > above mentioned is just my opinion, i need your advice and confirmation or
> > > deny
> > > 
> > > any help is appreciated.
> > > 
> > > 
> > > Regards
> > > 
> > > wanjia
> > 
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-devel
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel





_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel