How do correct mysqld.log error messages on start up?

I'm running Plesk and CentOS 6.7 Following is the excerpt of the log file mysqld.log when I restart mysqld service. I normally don't check this log file, but I just noticed some errors messages. It could have been there for a long time already. This is a live production server up and running for a couple of months, and I don't want to run anything destructive that can potentially jeopardize the stability and data integrity of the server. 170207 13:29:52 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql 170207 13:29:52 [Note] libgovernor.so not found 170207 13:29:52 [Note] /usr/libexec/mysqld (mysqld 5.5.44-cll-lve) starting as process 20524 ... 170207 13:29:52 [Note] Plugin 'FEDERATED' is disabled. 170207 13:29:52 InnoDB: The InnoDB memory heap is disabled 170207 13:29:52 InnoDB: Mutexes and rw_locks use GCC atomic builtins 170207 13:29:52 InnoDB: Compressed tables use zlib 1.2.3 170207 13:29:52 InnoDB: Using Linux native AIO 170207 13:29:52 InnoDB: Initializing buffer pool, size = 16.0G 170207 13:29:53 InnoDB: Completed initialization of buffer pool 170207 13:29:53 InnoDB: highest supported file format is Barracuda. 170207 13:29:54 InnoDB: Waiting for the background threads to start 170207 13:29:55 InnoDB: 5.5.44 started; log sequence number 408971509487 170207 13:29:55 [Note] Server hostname (bind-address): '127.0.0.1'; port: 3306 170207 13:29:55 [Note] - '127.0.0.1' resolves to '127.0.0.1'; 170207 13:29:55 [Note] Server socket created on IP: '127.0.0.1'. 170207 13:29:55 [ERROR] Missing system table mysql.proxies_priv; please run mysql_upgrade to create it 170207 13:29:55 [ERROR] Native table 'performance_schema'.'events_waits_current' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'events_waits_history' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'events_waits_history_long' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'setup_consumers' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'setup_instruments' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'setup_timers' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'performance_timers' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'threads' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'events_waits_summary_by_thread_by_event_name' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'events_waits_summary_by_instance' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'events_waits_summary_global_by_event_name' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'file_summary_by_event_name' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'file_summary_by_instance' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'mutex_instances' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'rwlock_instances' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'cond_instances' has the wrong structure 170207 13:29:55 [ERROR] Native table 'performance_schema'.'file_instances' has the wrong structure 170207 13:29:55 [Note] Event Scheduler: Loaded 0 events 170207 13:29:55 [Note] /usr/libexec/mysqld: ready for connections. Version: '5.5.44-cll-lve' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server (GPL) by Atomicorp **Questions:** 1. Even with all these startup errors, MySQL is still up and running well. Is this going to cause any performance impact on current MySQL server performance? 2. Regarding to missing system table mysql.proxies_priv, is this critical? and can I safely run the suggested mysql_upgrade without damaging the existing database? 3. If I were to run mysql_upgrade, do I need to stop mysqld first? 4. How do I correct/repair all the performance_schema wrong structure error messages?