Re: [Xen-devel] request of blkfront may disorder after migration without waiting in suspend phase of migration

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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...).

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
> 
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> > http://lists.xensource.com/xen-devel
> 
> 
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