... not just implementing barriers in hardware but also full monitors, allowing the wave to be notified if a specific cache line is evicted from the L2 cache. What is this feature for? When do you need it?
The explanation is missing that the hardware also notifies you of modifications, which makes it useful for implementing cross-cluster synchronization primitives.
Compare to MONITOR/MWAIT on x86: https://www.felixcloutier.com/x86/mwait#mwait-for-address-ra...