Figure 3 presents the latency of Barriers on 6,000 processes, depending on the rank of the initiator process that invokes the MPIX_COMM_REVOKE operation. Thanks to the symmetric nature of the BMG topology, the Revoked Barrier latency is stable and independent of the initiator rank.
One can note that the time to complete a Revoked Barrier is smaller than the time to complete a normal Barrier. The normal Barrier has a strong synchronizing semantic: the operation cannot complete before every process has entered the barrier. A Revoked Barrier doesn’t enforce that synchronization anymore and it can complete locally before some processes have participated. Instead, the latency of the Revoked operation denotes the time taken by the Revoke resilient broadcast to reach every rank for the first time; this propagation latency is similar to the cost of a small message Broadcast.