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

[Wang, Wei W]

On Thursday, May 18, 2023 4:52 PM, Wang, Lei4 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>
> ---
>  migration/socket.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/migration/socket.c b/migration/socket.c index
> 1b6f5baefb..b43a66ef7e 100644
> --- a/migration/socket.c
> +++ b/migration/socket.c
> @@ -179,7 +179,7 @@
> socket_start_incoming_migration_internal(SocketAddress *saddr,
>      QIONetListener *listener = qio_net_listener_new();
>      MigrationIncomingState *mis = migration_incoming_get_current();
>      size_t i;
> -    int num = 1;
> +    int num = 512;
> 

Probably we need a macro for it, e.g.
#define MIGRATION_CHANNEL_MAX  512

Also, I think below lines could be removed, as using a larger value of num 
(i.e. 512)
doesn't seem to consume more resources anywhere:
-    if (migrate_use_multifd()) {
-        num = migrate_multifd_channels();
-    } else if (migrate_postcopy_preempt()) {
-        num = RAM_CHANNEL_MAX;
-    }