Oracle: SQL to find CPU used percentage for each session

Select username,v.sid||','||v.serial# sid_session,round((s.value/y.value)*100,2) cpu_used_percentage
from v$session v, v$sesstat s,v$sysstat y
where v.username is not null
and v.sid = s.sid
and s.statistic#=y.statistic#
and y. name = 'CPU used by this session'
Order by username,3 desc