Query cache (size) 512 MB. Query cache size (query_cache_size) is over 128M. This may lead to a drop in performance. What to do with it?

Question

1C-Bitrix

Performance monitor: database server.

I got the following message:
Query cache (size) 512 MB. Query cache size (query_cache_size) is over 128M. This may lead to a drop in performance. What to do with it? What settings should be changed where?

And in the same place:

Query cache (efficiency) 0% If the cache efficiency is less than 20%, then it may be necessary to increase the value of the query_cache_limit parameter (current value: 16 MB)

query_cache_limit - what value should be set?