Manual browser: i386_pmc_read(2)

I386_PMC_INFO(2) System Calls Manual (i386) I386_PMC_INFO(2)


i386_pmc_info, i386_pmc_startstop, i386_pmc_readinterface to CPU performance counters


i386 Architecture Library (libi386, -li386)


#include <sys/types.h>
#include <machine/sysarch.h>
#include <machine/specialreg.h>

i386_pmc_info(struct i386_pmc_info_args *ia);

i386_pmc_startstop(struct i386_pmc_startstop_args *ssa);

i386_pmc_read(struct i386_pmc_read_args *ra);


These functions provide an interface to the CPU performance counters on the 586-class and 686-class processors.

i386_pmc_info() will return information about the available CPU counters. The information is returned in ia having the following structure:

struct i386_pmc_info_args { 
        int     type; 
        int     flags; 

The type member describes the class of performance counters available. Valid values are:

No PMC support
586-class CPUs
686-class Intel CPUs
686-class AMD CPUs

The flags member describes additional capabilities of the processor. Valid values are:

CPU has time-stamp counter

i386_pmc_startstop() is used to start and stop the measurement of the CPU performance counters. The argument ssa has the following structure:

struct i386_pmc_startstop_args { 
        int counter; 
        uint64_t val; 
        uint8_t event; 
        uint8_t unit; 
        uint8_t compare; 
        uint8_t flags; 

The counter specified by the member counter is started if the member flags has PMC_SETUP_KERNEL or PMC_SETUP_USER set, otherwise the counter is stopped. The initial value of the counter is set to val. Additional values for the flags member are PMC_SETUP_EDGE and PMC_SETUP_INV. The event member specifies some event written to the control register. The unit member specifies the measurement units. The compare member is a mask for the counter.

i386_pmc_read() will return information about a specific CPU counter measured during the last measurement period determined by the calling of i386_pmc_startstop(). The information is returned in ra having the following structure:

struct i386_pmc_read_args { 
        int counter; 
        uint64_t val; 
        uint64_t time; 

The counter to read should be specified by the counter member. Counters are numbered from 0 to PMC_NCOUNTERS. The value of the counter is returned in the val member. The time since epoch, measured in CPU clock cycles, is returned in the time member.


Upon successful completion zero is returned, otherwise -1 is returned on failure.
November 10, 2001 NetBSD 7.0