thread_cache_size

The thread cache hit rate can be calculated with Threads_created/Connections. Ideally you want the threads cached to be able to handle all connections. So a stable (zero growth) or low Threads_created status variable is the goal.

Depending on your specific situation, in some case this value can be very high (like 150+).
For an idea of the value needed, check the status variable Max_used_connections. If possible have thread_cache_size equal to the peak Max_used_connections value