In experiments conducted some years ago, I determined that the most efficient way to signal between two guests was to use alternating IUCV QUIESCE and RESUME signals. These signals cause the target to receive an IUCV external interruption, which is sufficient to let it know that something has changed. I can't say that this is still the case, but it se ems likely that avoiding the data transfer associated with SEND would make th is approach slightly more efficient.
Romney White
