RCU_FANOUT_2
#define RCU_FANOUT_3 (RCU_FANOUT_2 * RCU_FANOUT)
#elif NR_CPUS <= RCU_FANOUT_2
# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)