PERFMON(4)                                               BSD/i386 Kernel Interfaces Manual                                              PERFMON(4)

NAME

     perfmon -- CPU performance-monitoring interface

SYNOPSIS

     cpu I586_CPU
     cpu I686_CPU
     options PERFMON

DESCRIPTION

     The perfmon driver provides access to the internal performance-monitoring capabilities of the Intel Pentium and Pentium Pro CPUs.  These pro-
     cessors implement two internal counters which can be configured to measure a variety of events for either count or duration (in CPU cycles),
     as well as a cycle counter which counts clock cycles.  The perfmon driver provides a device-style interface to these capabilities.

     All access to the performance-monitoring counters is performed through the special device file ``/dev/perfmon''.  This device supports a num-
     ber of ioctl(2) requests, defined in <machine/perfmon.h> along with the definitions of the various counters for both Pentium and Pentium Pro
     processors.

     NOTA BENE: The set of available events differs from processor to processor.  It is the responsibility of the programmer to ensure that the
     event numbers used are the correct ones for the CPU type being measured.

     The following ioctl(2) requests are defined:

     PMIOSETUP   (struct pmc) Set up a counter with parameters and flags defined in the structure.  The following fields are defined in struct
                 pmc:

                 int pmc_num        the number of the counter in question; must be less than NPMC (currently 2).

                 u_char pmc_event   the particular event number to be monitored, as defined in <machine/perfmon.h>.

                 u_char pmc_unit    the unit mask value, specific to the event type (see the Intel documentation).

                 u_char pmc_flags   flags modifying the operation of the counter (see below).

                 u_char pmc_mask    the counter mask value; essentially, this is a threshold used to restrict the count to events lasting more (or
                                    less) than the specified number of clocks.

                 The following pmc_flags values are defined:
                 PMCF_USR    count events in user mode
                 PMCF_OS     count events in kernel mode
                 PMCF_E      count number of events rather than their duration
                 PMCF_INV    invert the sense of the counter mask comparison

     PMIOGET     (struct pmc) returns the current configuration of the specified counter.

     PMIOSTART

     PMIOSTOP    (int) starts (stops) the specified counter.  Due to hardware deficiencies, counters must be started and stopped in numerical
                 order.  (That is to say, counter 0 can never be stopped without first stopping counter 1.)  The driver will not enforce this
                 restriction (since it may not be present in future CPUs).

     PMIORESET   (int) reset the specified counter to zero.  The counter should be stopped with PMIOSTOP before it is reset.  All counters are
                 automatically reset by PMIOSETUP.

     PMIOREAD    (struct pmc_data) get the current value of the counter.  The pmc_data structure defines two fields:

                 int pmcd_num       the number of the counter to read
                 quad_t pmcd_value  the resulting value as a 64-bit signed integer

                 In the future, it may be possible to use the RDPMC instruction on Pentium Pro processors to read the counters directly.

     PMIOTSTAMP  (struct pmc_tstamp) read the time stamp counter.  The pmc_tstamp structure defines two fields:

                 int pmct_rate      the approximate rate of the counter, in MHz
                 quad_t pmct_value  the current value of the counter as a 64-bit integer

                 It is important to note that the counter rate, as provided in the pmct_rate field, is often incorrect because of calibration dif-
                 ficulties and non-integral clock rates.  This field should be considered more of a hint or sanity-check than an actual represen-
                 tation of the rate of clock ticks.

FILES

     /dev/perfmon                    character device interface to counters
     /usr/include/machine/perfmon.h  include file with definitions of structures and event types
     /usr/share/examples/perfmon     sample source code demonstrating use of all the ioctl() commands

SEE ALSO

     ioctl(2), hwpmc(4)

     Intel Corporation, Pentium Pro Family Developer's Manual, vol. 3, January 1996, Operating System Writer's Manual.

HISTORY

     The perfmon device first appeared in FreeBSD 2.2.

AUTHORS

     The perfmon driver was written by Garrett A. Wollman, MIT Laboratory for Computer Science.

BSD                                                               March 26, 1996                                                               BSD