Hello, when i use command top i can see list of proccess. I can see Code: 219406 web3 20 0 196172 28976 18400 S 1.3 0.1 0:00.05 php-fpm+ 12 root 20 0 0 0 0 I 0.3 0.0 1:14.91 rcu_sch+ 233 root 20 0 0 0 0 S 0.3 0.0 0:05.19 jbd2/sd+ 526 memcache 20 0 433972 31068 2312 S 0.3 0.1 2:26.02 memcach+ 567 root 20 0 1433288 32220 9952 S 0.3 0.1 5:28.27 fail2ba+ 693 mysql 20 0 3688080 1.2g 23048 S 0.3 3.9 19:11.73 mariadbd 208239 www-data 20 0 3545016 43588 11320 S 0.3 0.1 0:42.97 /usr/sb+ 219300 root 20 0 12680 3700 3088 R 0.3 0.0 0:00.11 top 1 root 20 0 164268 10548 7708 S 0.0 0.0 0:22.57 systemd 2 root 20 0 0 0 0 S 0.0 0.0 0:00.04 kthreadd 3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp 4 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_par+ 6 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker+ 8 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mm_perc+ 9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_tas+ 10 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_tas+ 11 root 20 0 0 0 0 S 0.0 0.0 0:00.68 ksoftir+ Is here anybody who can tell me why for example in 3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp is "-20". What does it mean?
You omitted column headers from the listing you posted. That would help deciphering the output. In line Code: 3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp the 4th column with value -20 has header NI, which means "nice value", I learned this from reading the top man page.
Nice values are user-space values that we can use to control the priority of a process. The nice value range is -20 to +19 where -20 is highest, 0 default and +19 is lowest. So -20 means these are very high priority processes. However keep in mind the nice value is a user-space value. The kernel itself has a value called "priority value" to control this. In your example the process RCU is a kernel synchronization mechanism, and as a result should have the highest priority.
