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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 perfor mance-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 cy cles), 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 per formed through
the special device file ‘‘/dev/perfmon’’. This device sup ports a number
of ioctl(2) requests, defined in #include <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 proces sor 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 (cur rently 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
documen tation).

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

u_char pmc_mask
the counter mask value; es sentially, this is a threshold used to re strict 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 re set. 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 coun ters 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 sanitycheck than an
actual representation of the rate of clock ticks.

Files

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

See Also

ioctl(2)

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

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