low_overhead_timers.h

// Some timers
//
// rdtsc() returns the number of "nominal" processor cycles since the system booted in a 64-bit unsigned integer.
//       For all recent Intel processors, this counter increments at a fixed rate, independent of the actual
//       core clock speed or the energy-saving mode.
// rdtscp() is the same as rdtsc except that it is partially ordered -- it will not execute until all prior
//       instructions in program order have executed.  (See also full_rdtscp)
// full_rdtscp() returns the number of "nominal" processor cycles in a 64-bit unsigned integer and also 
//       modifies its two integer arguments to show the processor socket and processor core that were in use
//       when the call was made.  (Note: the various cores in a chip usually have very similar values for 
//       the TSC, but they are allowed to vary by processor.  This function guarantees that you know exactly
//       which processor the TSC reading came from.)
// get_core_number() uses the RDTSCP instruction, but returns only the core number in an integer variable.
// get_socket_number() uses the RDTSCP instruction, but returns only the socket number in an integer variable.
// rdpmc_instructions() uses a "fixed-function" performance counter to return the count of retired instructions on
//       the current core in the low-order 48 bits of an unsigned 64-bit integer.
// rdpmc_actual_cycles() uses a "fixed-function" performance counter to return the count of actual CPU core cycles
//       executed by the current core.  Core cycles are not accumulated while the processor is in the "HALT" state,
//       which is used when the operating system has no task(s) to run on a processor core.
// rdpmc_reference_cycles() uses a "fixed-function" performance counter to return the count of "reference" (or "nominal")
//       CPU core cycles executed by the current core.  This counts at the same rate as the TSC, but does not count
//       when the core is in the "HALT" state.  If a timed section of code shows a larger change in TSC than in
//       rdpmc_reference_cycles, the processor probably spent some time in a HALT state.
// rdpmc() reads the programmable core performance counter number specified in the input argument.
//		 No error or bounds checking is performed.
//
// get_TSC_frequency() parses the Brand Identification string from the CPUID instruction to get the "nominal"
//       frequency of the processor, which is also the invariant TSC frequency, and returned as a float value in Hz.
//       This can then be used to convert TSC cycles to seconds.
//

unsigned long rdtsc();
unsigned long rdtscp();
unsigned long full_rdtscp(int *chip, int *core);
int get_core_number();
int get_socket_number();
unsigned long rdpmc_instructions();
unsigned long rdpmc_actual_cycles();
unsigned long rdpmc_reference_cycles();
unsigned long rdpmc(int c);
int get_core_counter_width();
unsigned long corrected_pmc_delta(unsigned long end, unsigned long start, int pmc_width);
float get_TSC_frequency();