Also, see these important notes in 100% CPU utilization. 

The DB CPU Oracle metric is the amount of CPU time (in microseconds) spent on database user-level calls. This does not include the CPU time spent on instance background processes such as PMON.

The most important time model statistics are DB time and DB CPU . The DB time statistic shows the elapsed processing time accumulated from the elapsed times of non-idle sessions. DB CPU presents the cumulative CPU time from all non-idle sessions. Both statistics directly show database workload and describe overall database response time.

The most important statistics within the time model views are DB time and DB CPU. The DB time statistic in the v$sess_time_model view determines the total elapsed processing time spent by database for a particular session.

You will also see the DB CPU statistic in the v$sys_time_model view represents the total cumulative time spent by Oracle for all sessions’ CPU times and wait times spent for non-idle wait events. Therefore, the system-wide DB CPU time can exceed the elapsed time since the last instance startup.  Use the following script to retrieve DB CPU statistics available in v$sys_time_model:

select
stat_name,
Round(value/1000000) "Time (Sec)"
from v$sys_time_model
where stat_name = 'DB CPU';


STAT_NAME Time (Sec)

------------------------------------------ ----------

DB CPU 299,352

Inside Oracle, you can display CPU for any Oracle user session with this script:

select
   ss.username,
   se.SID,
   VALUE/100 cpu_usage_seconds
from
   v$session ss,
   v$sesstat se,
   v$statname sn
where
   se.STATISTIC# = sn.STATISTIC#
and
   NAME like '%CPU used by this session%'
and
   se.SID = ss.SID
and
   ss.status='ACTIVE'
and
   ss.username is not null
order by VALUE desc;

For complete scripts to monitor CPU, see the Oracle script download.