Optimizing MySQL suggestions?

hi When the number of users increases, the speed drops sharply. please Help me Current my.cnf : *********************************** [mysqld] datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock skip-external-locking key_buffer_size = 8G wait_timeout=100 max_allowed_packet = 16M table_open_cache = 5120 sort_buffer_size = 16M net_buffer_length = 2K read_buffer_size = 16M read_rnd_buffer_size = 8M myisam_sort_buffer_size = 1G thread_cache_size = 512 query_cache_type=1 query_cache_size = 512M tmp_table_size = 512M #skip-networking max_connections = 550 max_connect_errors = 100 open_files_limit = 65535 log-bin=mysql-bin binlog_format=mixed server-id = 1 expire_logs_days = 1 max_binlog_size = 1000M interactive_timeout=50 connect_timeout=10 join_buffer=1M max_connect_errors=10 record_buffer=1M thread_concurrency = 40 skip-innodb [myisamchk] key_buffer=512M sort_buffer=256M read_buffer=16M write_buffer=16M user=mysql # Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0 [mysqld_safe] log-error=/var/log/mysqld.log pid-file=/var/run/mysqld/mysqld.pid *********************************************** CPU Model [20Core] : Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz | Frequency:1995.192 | Secondary cache:20480 KB | Bogomips:3990.38 "20 Total Memory: 60 G Server OS : Linux Kernel version: 2.6.32-504.el6.x86_64 Web Server : LiteSpeed **************************************************** all my tables : myisam tables numbers : 30 total records : 30M
Thank you