[Samba] High CPU usage by rpc_server

[Karan Blas]

We have two Samba AD-DC.

One is version 4.5.12 (debian) and 4.5.11 (ubuntu). On both, the rpc_server is using one core to the max 99-100% all the time.

I see the PID by samba-tool processes and I see something like 

dnsupdate              19526
cldap_server           19520
rpc_server             19515
rpc_server             19515
rpc_server             19515
rpc_server             19515
rpc_server             19515
nbt_server             19517
winbind_server         19528
kdc_server             19521
notify-daemon          19531
ldap_server            19519
kccsrv                 19525
samba                      0
dreplsrv               19522
dnssrv                 19527


The situation is same even at night with low load and if I shutdown one of them there is also no much difference. However if I copy the server in isolated environment it is silent ..1-5% CPU. We have around 1000 users. Can it be from the clients? At night there are less then 5 connections to the Samba:

netstat -tunepv | grep samba | wc -l