Fortigate 90D High CPU Usage

Currently I'm running the Fortigate Firewall 90D as internet gateway, it's covering about 25 users to internet. I have a concern regarding the CPU usage. There is 99% utilization. I used the command "diag sys top" and I got the result as below.  The process "src-vis" using almost 48,2%. I have tried to disable the disk log setting. But it still high. Do you have any ideas?

         src-vis       88      R      48.2     0.9

         netscan      899      R      47.7     1.7

       ipsengine      122      S <     1.4     2.0

          newcli      902      R       0.9     0.9

       ipshelper       87      S <     0.0     1.9

         pyfcgid      118      S       0.0     1.7

         cmdbsvr       37      S       0.0     1.7

         miglogd      112      S       0.0     1.7

         pyfcgid       59      S       0.0     1.6

         pyfcgid      117      S       0.0     1.6

         pyfcgid      116      S       0.0     1.6

         miglogd       53      S       0.0     1.5

          httpsd      135      S       0.0     1.5

          httpsd      136      S       0.0     1.4

         sslvpnd       77      S       0.0     1.3

          cw_acd      107      S       0.0     1.3

          httpsd      900      S       0.0     1.3

          httpsd       58      S       0.0     1.3

          httpsd      134      S       0.0     1.2

       forticron       71      S       0.0     1.1