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PMC(3)                 FreeBSD Library Functions Manual                 PMC(3)

     pmc - library for accessing hardware performance monitoring counters

     Performance Counters Library (libpmc, -lpmc)

     #include <pmc.h>

     The Performance Counters Library (libpmc, -lpmc) provides a programming
     interface that allows applications to use hardware performance counters
     to gather performance data about specific processes or for the system as
     a whole.  The library is implemented using the lower-level facilities
     offered by the hwpmc(4) driver.

   Key Concepts
     Performance monitoring counters (PMCs) are represented by the library
     using a software abstraction.  These ``abstract'' PMCs can have two

        System scope.  These PMCs measure events in a whole-system manner,
         i.e., independent of the currently executing thread.  System scope
         PMCs are allocated on specific CPUs and do not migrate between CPUs.
         Non-privileged process are allowed to allocate system scope PMCs if
         the hwpmc(4) sysctl tunable: security.bsd.unprivileged_syspmcs is

        Process scope.  These PMCs only measure hardware events when the
         processes they are attached to are executing on a CPU.  In an SMP
         system, process scope PMCs migrate between CPUs along with their
         target processes.

     Orthogonal to PMC scope, PMCs may be allocated in one of two operational

        Counting PMCs measure events according to their scope (system or
         process).  The application needs to explicitly read these counters to
         retrieve their value.

        Sampling PMCs cause the CPU to be periodically interrupted and
         information about its state of execution to be collected.  Sampling
         PMCs are used to profile specific processes and kernel threads or to
         profile the system as a whole.

     The scope and operational mode for a software PMC are specified at PMC
     allocation time.  An application is allowed to allocate multiple PMCs
     subject to availability of hardware resources.

     The library uses human-readable strings to name the event being measured
     by hardware.  The syntax used for specifying a hardware event along with
     additional event specific qualifiers (if any) is described in detail in
     section EVENT SPECIFIERS below.

     PMCs are associated with the process that allocated them and will be
     automatically reclaimed by the system when the process exits.
     Additionally, process-scope PMCs have to be attached to one or more
     target processes before they can perform measurements.  A process-scope
     PMC may be attached to those target processes that its owner process
     would otherwise be permitted to debug.  An owner process may attach PMCs
     to itself allowing it to measure its own behavior.  Additionally, on some
     machine architectures, such self-attached PMCs may be read cheaply using
     specialized instructions supported by the processor.

     Certain kinds of PMCs require that a log file be configured before they
     may be started.  These include:

        System scope sampling PMCs.

        Process scope sampling PMCs.

        Process scope counting PMCs that have been configured to report PMC
         readings on process context switches or process exits.

     Up to one log file may be configured per owner process.  Events logged to
     a log file may be subsequently analyzed using the pmclog(3) family of

   Supported CPUs
     The CPUs known to the PMC library are named by the enum pmc_cputype
     enumeration.  Supported CPUs include:

     PMC_CPU_AMD_K7          AMD Athlon CPUs.
     PMC_CPU_AMD_K8          AMD Athlon64 CPUs.
     PMC_CPU_INTEL_ATOM      Intel Atom CPUs and other CPUs conforming to
                             version 3 of the Intel performance measurement
     PMC_CPU_INTEL_CORE      Intel Core Solo and Core Duo CPUs, and other CPUs
                             conforming to version 1 of the Intel performance
                             measurement architecture.
     PMC_CPU_INTEL_CORE2     Intel Core2 Solo, Core2 Duo and Core2 Extreme
                             CPUs, and other CPUs conforming to version 2 of
                             the Intel performance measurement architecture.
     PMC_CPU_INTEL_P5        Intel Pentium CPUs.
     PMC_CPU_INTEL_P6        Intel Pentium Pro CPUs.
     PMC_CPU_INTEL_PII       Intel Pentium II CPUs.
     PMC_CPU_INTEL_PIII      Intel Pentium III CPUs.
     PMC_CPU_INTEL_PIV       Intel Pentium 4 CPUs.
     PMC_CPU_INTEL_PM        Intel Pentium M CPUs.

   Supported PMCs
     PMC supported by this library are named by the enum pmc_class
     enumeration.  Supported PMC kinds include:

     PMC_CLASS_IAF     Fixed function hardware counters presents in CPUs
                       conforming to the Intel performance measurement
                       architecture version 2 and later.
     PMC_CLASS_IAP     Programmable hardware counters present in CPUs
                       conforming to the Intel performance measurement
                       architecture version 1 and later.
     PMC_CLASS_K7      Programmable hardware counters present in AMD Athlon
     PMC_CLASS_K8      Programmable hardware counters present in AMD Athlon64
     PMC_CLASS_P4      Programmable hardware counters present in Intel Pentium
                       4 CPUs.
     PMC_CLASS_P5      Programmable hardware counters present in Intel Pentium
     PMC_CLASS_P6      Programmable hardware counters present in Intel Pentium
                       Pro, Pentium II, Pentium III, Celeron, and Pentium M
     PMC_CLASS_TSC     The timestamp counter on i386 and amd64 architecture
     PMC_CLASS_SOFT    Software events.

   PMC Capabilities
     Capabilities of performance monitoring hardware are denoted using the
     enum pmc_caps enumeration.  Supported capabilities include:

     PMC_CAP_CASCADE       The ability to cascade counters.
     PMC_CAP_EDGE          The ability to count negated to asserted
                           transitions of the hardware conditions being probed
     PMC_CAP_INTERRUPT     The ability to interrupt the CPU.
     PMC_CAP_INVERT        The ability to invert the sense of the hardware
                           conditions being measured.
     PMC_CAP_PRECISE       The ability to perform precise sampling.
     PMC_CAP_QUALIFIER     The hardware allows monitored to be further
                           qualified in some system dependent way.
     PMC_CAP_READ          The ability to read from performance counters.
     PMC_CAP_SYSTEM        The ability to restrict counting of hardware events
                           to when the CPU is running privileged code.
     PMC_CAP_THRESHOLD     The ability to ignore simultaneous hardware events
                           below a programmable threshold.
     PMC_CAP_USER          The ability to restrict counting of hardware events
                           to those when the CPU is running unprivileged code.
     PMC_CAP_WRITE         The ability to write to performance counters.

   CPU Naming Conventions
     CPUs are named using small integers from zero up to, but excluding, the
     value returned by function pmc_ncpu().  On platforms supporting sparsely
     numbered CPUs not all the numbers in this range will denote valid CPUs.
     Operations on non-existent CPUs will return an error.

   Functional Grouping of the API
     This section contains a brief overview of the available functionality in
     the PMC library.  Each function listed here is described further in its
     own manual page.

         pmc_disable(), pmc_enable()
                 Administratively disable (enable) specific performance
                 monitoring counter hardware.  Counters that are disabled will
                 not be available to applications to use.

     Convenience Functions
                 Returns a list of event names supported by a given PMC type.
                 Convert a PMC_CAP_* flag to a human-readable string.
                 Convert a PMC_CLASS_* constant to a human-readable string.
                 Return a human-readable name for a CPU type.
                 Return a human-readable string describing a PMC's
                 Convert a numeric event code to a human-readable string.
                 Convert a PMC_MODE_* constant to a human-readable name.
                 Return a human-readable string describing a PMC's current

     Library Initialization
                 Initialize the library.  This function must be called before
                 any other library function.

     Log File Handling
                 Configure a log file for hwpmc(4) to write logged events to.
                 Flush all pending log data in hwpmc(4)'s buffers.
                 Flush all pending log data and close hwpmc(4)'s side of the
                 Append arbitrary user data to the current log file.

     PMC Management
         pmc_allocate(), pmc_release()
                 Allocate (free) a PMC.
         pmc_attach(), pmc_detach()
                 Attach (detach) a process scope PMC to a target.
         pmc_read(), pmc_write(), pmc_rw()
                 Read (write) a value from (to) a PMC.
         pmc_start(), pmc_stop()
                 Start (stop) a software PMC.
                 Set the reload value for a sampling PMC.

                 Retrieve the capabilities for a given PMC.
                 Retrieve information about the CPUs and PMC hardware present
                 in the system.
                 Retrieve statistics maintained by hwpmc(4).
                 Determine the greatest possible CPU number on the system.
                 Return the number of hardware PMCs present in a given CPU.
                 Return information about the state of a given CPU's PMCs.
                 Determine the width of a hardware counter in bits.

     x86 Architecture Specific API
                 Returns the processor model specific register number
                 associated with pmc.  Applications may then use the x86 RDPMC
                 instruction to directly read the contents of the PMC.

   Signal Handling Requirements
     Applications using PMCs are required to handle the following signals:

     SIGBUS      When the hwpmc(4) module is unloaded using kldunload(8),
                 processes that have PMCs allocated to them will be sent a
                 SIGBUS signal.

     SIGIO       The hwpmc(4) driver will send a PMC owning process a SIGIO
                 signal if:

                    If any process-mode PMC allocated by it loses all its
                     target processes.

                    If the driver encounters an error when writing log data
                     to a configured log file.  This error may be retrieved by
                     a subsequent call to pmc_flush_logfile().

   Typical Program Flow
     1.   An application would first invoke function pmc_init() to allow the
          library to initialize itself.

     2.   Signal handling would then be set up.

     3.   Next the application would allocate the PMCs it desires using
          function pmc_allocate().

     4.   Initial values for PMCs may be set using function pmc_set().

     5.   If a log file is necessary for the PMCs to work, it would be
          configured using function pmc_configure_logfile().

     6.   Process scope PMCs would then be attached to their target processes
          using function pmc_attach().

     7.   The PMCs would then be started using function pmc_start().

     8.   Once started, the values of counting PMCs may be read using function
          pmc_read().  For PMCs that write events to the log file, this logged
          data would be read and parsed using the pmclog(3) family of

     9.   PMCs are stopped using function pmc_stop(), and process scope PMCs
          are detached from their targets using function pmc_detach().

     10.  Before the process exits, its may release its PMCs using function
          pmc_release().  Any configured log file may be closed using function

     Event specifiers are strings comprising of an event name, followed by
     optional parameters modifying the semantics of the hardware event being
     probed.  Event names are PMC architecture dependent, but the PMC library
     defines machine independent aliases for commonly used events.

     Event specifiers spellings are case-insensitive and space characters,
     periods, underscores and hyphens are considered equivalent to each other.
     Thus the event specifiers "Example Event", "example-event", and
     "EXAMPLE_EVENT" are equivalent.

   PMC Architecture Dependent Events
     PMC architecture dependent event specifiers are described in the
     following manual pages:

     PMC Class          Manual Page
     PMC_CLASS_IAF      pmc.iaf(3)
     PMC_CLASS_IAP      pmc.atom(3), pmc.core(3), pmc.core2(3)
     PMC_CLASS_K7       pmc.k7(3)
     PMC_CLASS_K8       pmc.k8(3)
     PMC_CLASS_P4       pmc.p4(3)
     PMC_CLASS_P5       pmc.p5(3)
     PMC_CLASS_P6       pmc.p6(3)
     PMC_CLASS_TSC      pmc.tsc(3)

   Event Name Aliases
     Event name aliases are PMC-independent names for commonly used events.
     The following aliases are known to this version of the pmc library:

             Measure the number of branches retired.

             Measure the number of retired branches that were mispredicted.

     cycles  Measure processor cycles.  This event is implemented using the
             processor's Time Stamp Counter register.

             Measure the number of data cache misses.

             Measure the number of instruction cache misses.

             Measure the number of instructions retired.

             Measure the number of interrupts seen.

             Measure the number of cycles the processor is not in a halted or
             sleep state.

     The interface between the pmc library and the hwpmc(4) driver is intended
     to be private to the implementation and may change.  In order to ease
     forward compatibility with future versions of the hwpmc(4) driver,
     applications are urged to dynamically link with the pmc library.

     The pmc API is currently under development.

     pmc.atom(3), pmc.core(3), pmc.core2(3), pmc.haswell(3), pmc.haswelluc(3),
     pmc.haswellxeon(3), pmc.iaf(3), pmc.ivybridge(3), pmc.ivybridgexeon(3),
     pmc.k7(3), pmc.k8(3), pmc.mips24k(3), pmc.octeon(3), pmc.p4(3),
     pmc.p5(3), pmc.p6(3), pmc.sandybridge(3), pmc.sandybridgeuc(3),
     pmc.sandybridgexeon(3), pmc.soft(3), pmc.tsc(3), pmc.westmere(3),
     pmc.westmereuc(3), pmc.xscale(3), pmclog(3), hwpmc(4), pmccontrol(8),

     The pmc library first appeared in FreeBSD 6.0.

     The Performance Counters Library (libpmc, -lpmc) library was written by
     Joseph Koshy <[email protected]>.

FreeBSD 11.1-RELEASE-p4          July 28, 2014         FreeBSD 11.1-RELEASE-p4
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