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     perfmon — CPU performance-monitoring interface


     cpu I586_CPU
     cpu I686_CPU
     options PERFMON


     The perfmon driver provides access to the internal performance-monitoring capabilities of
     the Intel Pentium and Pentium Pro CPUs.  These processors 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 number 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

                 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.


     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 difficulties and non-integral
                 clock rates.  This field should be considered more of a hint or sanity-check
                 than an actual representation of the rate of clock ticks.


     /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()


     ioctl(2), hwpmc(4)

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


     The perfmon device first appeared in FreeBSD 2.2.


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