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


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 pro- vides 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 defi- nitions of the various counters for both Pentium and Pentium Pro proces- sors. NOTA BENE: The set of available events differs from processor to proces- sor. 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 moni- tored, 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 speci- fied counter. PMIOSTART PMIOSTOP (int) starts (stops) the specified counter. Due to hardware deficiencies, counters must be started and stopped in numeri- cal 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 instruc- tion 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 calibra- tion 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 <machine/perfmon.h> include file with definitions of struc- tures and event types /usr/share/examples/perfmon sample source code demonstrating use of all the ioctl() commands


ioctl(2) 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. DragonFly 4.1 March 26, 1996 DragonFly 4.1

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