The csync instruction permits synchronization of the various CPUs of an organism. When a CPU executes the csync, it will stop executing and wait (loosing its time slice(s)), until all of the CPUs of the organism have also executed the csync instruction. When all of the CPUs have executed the csync instruction, then they will all simultaneously begin executing again.
At present, csync is an all-or-nothing synchronization. There is no mechanism to permit a sub-set of the CPUs to synchronize independently from the other CPUs of an organism.