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NAME    [Toc]    [Back]

     perfmon -- CPU performance-monitoring interface

SYNOPSIS    [Toc]    [Back]

     cpu I586_CPU
     cpu I686_CPU
     options PERFMON

DESCRIPTION    [Toc]    [Back]

     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 <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


     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

		 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
		 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.

FILES    [Toc]    [Back]

     /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    [Toc]    [Back]


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

HISTORY    [Toc]    [Back]

     The perfmon device first appeared in FreeBSD 2.2.

AUTHORS    [Toc]    [Back]

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

FreeBSD 5.2.1			March 26, 1996			 FreeBSD 5.2.1
[ Back ]
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