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

To: alice wan <wanjia19870902@xxxxxxxxx>
Subject: Re: [Xen-devel] request of blkfront may disorder after migration without waiting in suspend phase of migration
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Tue, 12 Jul 2011 14:23:35 -0400
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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?

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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