RE: [PATCH v2 2/2] qtest/migration-tests.c: use "-incoming defer" for postcopy tests

[Wang, Wei W]

On Wednesday, May 31, 2023 8:58 PM, Peter Xu wrote:
> > > Hmm.. so we used to do socket_start_incoming_migration_internal()
> > > before setting the right num for the preempt test, then I'm curious
> > > why it wasn't failing before this patch when trying to connect with the
> preempt channel..
> > >
> > > Wei, do you know?
> >
> > I think there are two reasons:
> > #1 "backlog" specifies the number of pending connections. As long as
> > the server accepts the connections faster than the clients side
> > connecting, connection will succeed. For the preempt test, it uses
> > only 2 channels, so very likely to not have pending connections. (This
> > is easier to trigger for the multifd case, e.g. use a much larger number 
> > like
> 16).
> > #2 per my tests (on kernel 6.2), the number of pending connections
> > allowed is actually "backlog + 1", which is 2 in this case. Adding
> > more pending connections will then be dropped. I'm not sure if " backlog +
> 1" is true for older versions of kernel, though.
> 
> Interesting to know, thanks.
> 
> If there'll be a new version, please consider adding some of those into the
> commit message.

OK, will resend with commit update.
Plan to wait a bit in case there would be other feedbacks.

> 
> Reviewed-by: Peter Xu <peterx@redhat.com>
> 
> --
> Peter Xu