high cpu load because high CPU time for sys

I am using MariaDB galera cluster with two nodes + one node for arbiter. My system has 24 core CPU. I am getting stuck with CPU bound. Sometimes, my system consume CPU time to 1000% and CPU load get above 16. Mysqld process consume about 200-300% and noramlly CPU load is about 2-3.

I am monitoring process list. I don't know why some system process like md126_raid1, irqbalance... suddenly consume CPU so much. There is nothing in /var/log/messages or dmesg. I am running multi master on galera so there is some conflict in error messages of mysqld but I think it is natural and mysqld not consume CPU so much.

Do you know any ideas for my problem ?

P/S: Sorry if my english is not good.