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Subject: [Qemu-devel] Re: Live migration broken when under heavy IO
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, kvm-devel <kvm@vger.kernel.org>

On 06/15/2009 11:33 PM, Anthony Liguori wrote:
> The basic issue is that:
>
> migrate_fd_put_ready():    bdrv_flush_all();
>
> Does:
>
> block.c:
>
> foreach block driver:
>   drv->flush(bs);
>
> Which in the case of raw, is just fsync(s->fd).
>
> Any submitted request is not queued or flushed which will lead to the 
> request being dropped after the live migration.
>
> Is anyone working on fixing this? 

Not to my knowledge

> Does anyone have a clever idea how to fix this without just waiting 
> for all IO requests to complete?

What's wrong with waiting for requests to complete?  It should take a 
few tens of milliseconds.

We could start throttling requests late in the live stage, but I don't 
really see the point.

Isn't virtio migration currently broken due to the qdev changes?

-- 
error compiling committee.c: too many arguments to function