ppc64 oprofile on IBM i series

In arch/ppc64/kernel/time.c:timer_interrupt There is the following ifndef:

#ifndef CONFIG_PPC_ISERIES
        ppc64_do_profile(regs);

#endif

I got access to a i series machine and tried a kernel with the surrounding ifndef removed to test whether the oprofile support would work on a i series machine. OProfile appears to work. Is there some reason that it is disabled for i series machines, e.g. doesn't work on particular i series machines?

-Will