RE: [PATCH] multifd: Set a higher "backlog" default value for listen()

[Wang, Wei W]

On Friday, May 19, 2023 9:31 AM, Wang, Lei4 wrote:
> On 5/18/2023 17:16, Juan Quintela wrote:
> > Lei Wang <lei4.wang@intel.com> wrote:
> >> When destination VM is launched, the "backlog" parameter for listen()
> >> is set to 1 as default in socket_start_incoming_migration_internal(),
> >> which will lead to socket connection error (the queue of pending
> >> connections is full) when "multifd" and "multifd-channels" are set
> >> later on and a high number of channels are used. Set it to a
> >> hard-coded higher default value 512 to fix this issue.
> >>
> >> Reported-by: Wei Wang <wei.w.wang@intel.com>
> >> Signed-off-by: Lei Wang <lei4.wang@intel.com>
> >
> > [cc'd daiel who is the maintainer of qio]
> >
> > My understanding of that value is that 230 or something like that
> > would be more than enough.  The maxiimum number of multifd channels is
> 256.
> 
> You are right, the "multifd-channels" expects uint8_t, so 256 is enough.
> 

We can change it to uint16_t or uint32_t, but need to see if listening on a 
larger
value is OK to everyone.

Man page of listen mentions that the  maximum length of the queue for
incomplete sockets can be set using /proc/sys/net/ipv4/tcp_max_syn_backlog,
and it is 4096 by default on my machine.