smp_processor_id()/cpu_[number/logical]_map() include/asm/smp.h

smp_processor_id() returns the current processor number, between 0 and NR_CPUS (the maximum number of CPUs supported by Linux, currently 32). These values are not necessarily continuous: to get a number between 0 and smp_num_cpus() (the number of actual processors in this machine), the cpu_number_map() function is used to map the processor id to a logical number. cpu_logical_map() does the reverse.