Receiving the error "Can't resolve rq struct in sched_switch tracepoint" using systemtap on RHEL5

Issue

• I was trying to create a script to profile the scheduler and I wanted to know which cpu the sched_switch function was being on.  I looked at the sched_switch tracepoint and saw that it has a struct rq, which should contain a member variable "int cpu".

• When I try to use it, I get an error on the console:

  [root@lab300g5 ~]# stap -L 'kernel.trace("sched_switch")'
  kernel.trace("sched_switch") 
  $rq:struct rq* $prev:struct task_struct* $next:struct task_struct*
  
  semantic error: unresolved struct rq: identifier '$rq' at lookAtRq.stp:2:8
          source:         cpu = $rq->cpu;
                                ^
  Pass 2: analysis failed.  Try again with another '--vp 01' option.