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Date: Tue, 03 Sep 2013 10:13:54 -0400
From: "Michael R. Hines" <mrhines@linux.vnet.ibm.com>
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Subject: Re: [Qemu-devel] [Qemu-stable][PATCH] rdma: fix multiple
 VMs	parallel migration
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To: Frank Yang <frank.yangjie@gmail.com>
Cc: Isaku Yamahata <yamahata@private.email.ne.jp>, qemu-stable@nongnu.org, qemu-devel@nongnu.org, yamahata@valinux.co.jp, Michael R Hines <mrhines@us.ibm.com>, pbonzini@redhat.com


No top-posting, please.

On 09/03/2013 12:20 AM, Frank Yang wrote:
> Yes, it depends on low-level implementation. During my earlier test,
> using one CQ to send and receive may cause packet loss with heavy load:
> the destination thinks it send READY message successfully but the source
> still waits for it. This situation always happens when the destination 
> polls
> receive CQE first.
>
> So I think using only one CQ may cause packet conflict or something 
> like that,
> and it should be the driver bug. However, using two CQs fix the problem.
>
>

This doesn't seem like a very clear answer ..... are you sure its packet 
loss?

The queue pairs are supposed to be reliable - I've never experienced a 
situation
where packets were simply "dropped" for no reason without breaking the
connection and putting the QP into an error state.

- Michael