How to understand why CentOS lags for no apparent reason?

Question

CentOS

There seems to be nothing criminal in top.

But the whole system screams that it is terribly busy, the lags are wild.
How to understand what is the reason?
Everything is slow - reading from disk, installing in yum, switching columns in top.
UPD

Answer 1

Thank you all for your help.
It turned out that a rootkit was wound up on the server, which launched a bitcoin miner for all 8 cores.
How exactly he got on the server, I don’t know yet, how I will find out, I will fence myself off.
Here it is discussed www.webhostingtalk.com/showthread.php?t=1512831
And here is a brief instruction on how to remove www.ipserverone.info/uncategorized/server-abnormal...
Thanks for the key tip ldv

Answer 2

what are the characteristics of the system? la at 40 blindly difficult to evaluate + look at what queue for writing / reading is worth. maybe the disk system is killing performance. it was similar when I deployed a huge zabbix to mysql on not high-speed disks at all - a huge queue lined up to write data
[upd] iostat output what?

Answer 3

Duc you have mv spinning, which somewhere figachit the base of the muscle. Between filesystems, probably. Working, probably. It slows it down.

Answer 4

Openvz maybe?
Neighbors spent the entire CPU.