“We measure the latency it takes for a CPU to send a message to another CPU via its cache coherence protocol.”
An old Core i9-9900K passes a message between cores in 21 nanoseconds. A Ryzen 9 7950X takes 68. The M1 Pro hits about 145 across core groups, which is dual-socket territory. More cores on the box do not help when your threads keep talking to each other.