In terms of cycles the switch has become more expensive since a lot of registers were added that need saving/restoring. (But since frequencies have increased a

In terms of cycles the switch has become more expensive since a lot of registers were added that need saving/restoring. (But since frequencies have increased a lot the absolute time shrank when we reached the "3 GHz era"; I think it's been pretty much constant for the last ~10 years or so). But you are right that the switch itself on modern-era (=32+ bit few-chip systems with MMU) hardware was never really that expensive (on the order of 10-20 us).