Re: [Qemu-devel] [PATCH 6/6] RFH: We lost "connect" events

[Juan Quintela <quintela@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> wrote:
> On Wed, Aug 14, 2019 at 04:02:18AM +0200, Juan Quintela wrote:
>> When we have lots of channels, sometimes multifd migration fails
>> with the following error:
>>   after some time, sending side decides to send another packet through
>>   that channel, and it is now when we get the above error.
>> 
>> Any good ideas?
>
> In inet_listen_saddr() we call
>
>     if (!listen(slisten, 1)) {
>
> note the second parameter sets the socket backlog, which is the max
> number of pending socket connections we allow. My guess is that the
> target QEMU is not accepting incoming connections quickly enough and
> thus you hit the limit & the kernel starts dropping the incoming
> connections.
>
> As a quick test, just hack this code to pass a value of 100 and see
> if it makes your test reliable. If it does, then we'll need to figure
> out a nice way to handle backlog instead of hardcoding it at 1.

I will test.

But notice that the qemu_connect() on source side says that things went
right.  It is the destination what is *not* calling the callback.  Or
at least that is what I think it is happening.

Later, Juan.