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Date: Wed, 14 May 2014 15:46:48 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] e1000/rtl8139: forbid dealing with packets
 when VM is paused
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Zhouxiangjiu <zhouxiangjiu@huawei.com>, Peter Maydell <peter.maydell@linaro.org>, Peter Crosthwaite <peter.crosthwaite@xilinx.com>, Zhanghailiang <zhang.zhanghailiang@huawei.com>, Juan Quintela <quintela@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>, Alex Williamson <alex.williamson@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Amos Kong <akong@redhat.com>, Dave Gilbert <dgilbert@redhat.com>

On Wed, May 14, 2014 at 02:30:26PM +0200, Stefan Hajnoczi wrote:
> On Thu, May 08, 2014 at 12:51:05PM +0000, Zhanghailiang wrote:
> > > If you implement this in the net layer then that problem is easy to resolve since
> > > we can flush all queues when the guest resumes to get packets flowing again.
> > > 
> > Do you mean we should also listen for VM runstate changes in net layer, and when detect runstate changes back to running , we flush all queues actively? Am I misunderstanding? 
> > Or we can do it *before* qemu (exactly when it check if it can send packets) send packets to guest again, this way will be simple, but it also need know the change of runstate. Any idea? 
> 
> When the runstate changes back to running, we definitely need to flush
> queues to get packets flowing again.  I think the simplest way of doing
> that is in the net layer so individual NICs and netdevs don't have to
> duplicate this code.
> 
> Stefan

That will help with networking but not other devices.
The issue isn't limited to networking at all.
How about we stop all io threads with the vm?

That will address the issue in a generic way.

-- 
MST