An excellent article:
http://dboptimizer.com/2011/07/21/oracle-cpu-time/
Starting in 10g Oracle records both the CPU used by the instance as well as the load on the system in
v$sysmetric. This is awesome as we can see how busy the system is and how much of the CPU Oracle is responsible for:
col metric_name for a25
col metric_unit for a25
select metric_name, value, metric_unit from v$sysmetric where metric_name like'%CPU%' where group_id=2;
with AASSTAT as (
select
decode(n.wait_class,'User I/O','User I/O',
'Commit','Commit',
'Wait') CLASS,
sum(round(m.time_waited/m.INTSIZE_CSEC,3)) AAS
from v$waitclassmetric m,
v$system_wait_class n
where m.wait_class_id=n.wait_class_id
and n.wait_class != 'Idle'
group by decode(n.wait_class,'User I/O','User I/O', 'Commit','Commit', 'Wait')
union
select 'CPU_ORA_CONSUMED' CLASS,
round(value/100,3) AAS
from v$sysmetric
where metric_name='CPU Usage Per Sec'
and group_id=2
union
select 'CPU_OS' CLASS ,
round((prcnt.busy*parameter.cpu_count)/100,3) AAS
from
( select value busy from v$sysmetric where metric_name='Host CPU Utilization (%)' and group_id=2 ) prcnt,
( select value cpu_count from v$parameter where name='cpu_count' ) parameter
union
select
'CPU_ORA_DEMAND' CLASS,
nvl(round( sum(decode(session_state,'ON CPU',1,0))/60,2),0) AAS
from v$active_session_history ash
where SAMPLE_TIME > sysdate - (60/(24*60*60))
)
select
( decode(sign(CPU_OS-CPU_ORA_CONSUMED), -1, 0, (CPU_OS - CPU_ORA_CONSUMED )) +
CPU_ORA_CONSUMED +
decode(sign(CPU_ORA_DEMAND-CPU_ORA_CONSUMED), -1, 0, (CPU_ORA_DEMAND - CPU_ORA_CONSUMED ))) CPU_TOTAL,
decode(sign(CPU_OS-CPU_ORA_CONSUMED), -1, 0, (CPU_OS - CPU_ORA_CONSUMED )) CPU_OS,
CPU_ORA_CONSUMED CPU_ORA,
decode(sign(CPU_ORA_DEMAND-CPU_ORA_CONSUMED), -1, 0, (CPU_ORA_DEMAND - CPU_ORA_CONSUMED )) CPU_ORA_WAIT,
COMMIT,
READIO,
WAIT
from (
select
sum(decode(CLASS,'CPU_ORA_CONSUMED',AAS,0)) CPU_ORA_CONSUMED,
sum(decode(CLASS,'CPU_ORA_DEMAND' ,AAS,0)) CPU_ORA_DEMAND,
sum(decode(CLASS,'CPU_OS' ,AAS,0)) CPU_OS,
sum(decode(CLASS,'Commit' ,AAS,0)) COMMIT,
sum(decode(CLASS,'User I/O' ,AAS,0)) READIO,
sum(decode(CLASS,'Wait' ,AAS,0)) WAIT
from AASSTAT)
/
