how to reduce mysql overhead?
You use mytop and mysqltuner to analyze using mysql resources (RAM and CPU).

Too enable the option to log slow queries:

log_slow_queries = /var/log/mysql/mysql-slow.log
long_query_time = 3


And check out this post about ntpd service:

https://stackoverflow.com/questions/1282232/mysql-high-cpu-usage

I have a dedicated server for a high rate of transactions:

max_allowed_packet=16M
key_buffer_size=8M
innodb_additional_mem_pool_size=10M
innodb_buffer_pool_size=512M
join_buffer_size=40M
table_open_cache=1024
query_cache_size=40M
table_definition_cache=256
innodb_additional_mem_pool_size=10M
key_buffer_size=16M
max_allowed_packet=32M
max_connections = 300
query_cache_limit = 10M
log_slow_queries = /var/log/mysql/mysql-slow.log
long_query_time = 3


Regards.