PMC(9)                 NetBSD Kernel Developer's Manual                 PMC(9)

NAME
     pmc, pmc_get_num_counters, pmc_get_counter_type, pmc_save_context,
     pmc_restore_context, pmc_enable_counter, pmc_disable_counter,
     pmc_counter_isrunning, pmc_counter_isconfigured, pmc_configure_counter,
     pmc_get_counter_value, pmc_accumulate, pmc_alloc_kernel_counter,
     pmc_free_kernel_counter, pmc_start_profiling, pmc_stop_profiling,
     PMC_ENABLED -- Hardware Performance Monitoring Interface

SYNOPSIS
     #include <sys/pmc.h>

     int
     pmc_get_num_counters(void);

     int
     pmc_get_counter_type(int ctr);

     void
     pmc_save_context(struct lwp *l);

     void
     pmc_restore_context(struct lwp *l);

     int
     pmc_enable_counter(struct lwp *l, int ctr);

     int
     pmc_disable_counter(struct lwp *l, int ctr);

     int
     pmc_counter_isrunning(struct lwp *l, int ctr);

     int
     pmc_counter_isconfigured(struct lwp *l, int ctr);

     int
     pmc_configure_counter(struct lwp *l, int ctr,
         struct pmc_counter_cfg *cfg);

     int
     pmc_get_counter_value(struct lwp *l, int ctr, int flags, uint64_t *pval);

     int
     pmc_accumulate(struct lwp *l_parent, struct lwp *l_exiting);

     int
     pmc_alloc_kernel_counter(int ctr, struct pmc_counter_cfg *cfg);

     int
     pmc_free_kernel_counter(int ctr);

     int
     pmc_start_profiling(int ctr, struct pmc_counter_cfg *cfg);

     int
     pmc_stop_profiling(int ctr);

     int
     PMC_ENABLED(struct lwp *l);

DESCRIPTION
     Provides a machine-independent interface to the hardware performance
     counters which are available on several CPU families.  The capabilities
     of these counters vary from CPU to CPU, but they basically count hardware
     events such as data cache hits or misses, branches taken, branched mis-
     predicted, and so forth.  Some can interrupt the processor when a certain
     threshold has been reached.  Some can count events in user space and ker-
     nel space independently.

     The pmc interface is intended to allow monitoring from within the kernel
     as well as monitoring of userland applications.  If the hardware can
     interrupt the CPU in a specific implementation, then it may also be used
     as a profiling source instead of the clock.

IMPLEMENTATION NOTES
     All function calls in this interface may be defined as cpp(1) macros.  If
     any function is not implemented as a macro, its prototype must be defined
     by the port-specific header <machine/pmc.h>.

     Counters are numbered from 0 to N-1 where N is the number of counters
     available on the system (see pmc_get_num_counters() below).

     Upon a process fork, implementations must

        Zero performance counters for the new process, and

        Inherit any enabled performance counters.

DATA TYPES
     Each implementation must specify two new types:

     pmc_evid_t  An integer type which can contain the event IDs for a given
                 processor.

     pmc_ctr_t   An integer type defining the value which may be contained in
                 a given counter register.

     Counters are configured with the struct pmc_counter_cfg.  This structure
     is defined as

     struct pmc_counter_cfg {
             pmc_evid_t      event_id;
             pmc_ctr_t       reset_value;
             uint32_t        flags;
     };

     flags are currently unused.

FUNCTIONS
     pmc_get_num_counters(void)
            Returns the number of counters present on the current system.
            Valid values for ctr in the interface entry points below are from
            zero to one less than the return value from this function.

     pmc_get_counter_type(int ctr)
            Returns an implementation-dependent type describing the specified
            counter.  If ctr is specified as -1, returns a machine-dependent
            type describing the CPU or counter configuration.  For example, on
            an ia32 architecture, it may distinguish between 586-, 686-, and
            K7-style counters.

     pmc_save_context(struct lwp *l)
            Saves the PMC context for the current process.  This is called
            just before cpu_switch(9).  If there is kernel PMC state, it must
            be maintained across this call.

     pmc_restore_context(struct lwp *l)
            Restores the PMC context for the current process.  This is called
            just after cpu_switch(9) returns.  If there is kernel PMC state,
            it must be maintained across this call.

     pmc_enable_counter(struct lwp *l, int ctr)
            Enables counter ctr for the specified process.  The counter should
            have already been configured with a call to
            pmc_configure_counter().  This starts the counter running if it is
            not already started and enables any interrupts, as appropriate.

     pmc_disable_counter(struct lwp *l, int ctr)
            Disables counter ctr for the specified process.  This stops the
            counter from running, and disables any interrupts, as appropriate.

     pmc_counter_isrunning(struct lwp *l, int ctr)
            Returns non-zero if the specified counter in the specified process
            is running or if the counter is running in the kernel.

     pmc_counter_isconfigured(struct lwp *l, int ctr)
            Returns non-zero if the specified counter in the specified process
            is configured or if the counter is in use by the kernel.

     pmc_configure_counter(struct lwp *l, int ctr, struct pmc_counter_cfg
            *cfg)
            Configures counter ctr according to the configuration information
            stored in cfg.

     pmc_get_counter_value(struct lwp *l, int ctr, int flags, uint64_t *pval)
            Returns the value of counter ctr in the space pointed to by pval.
            The only recognized flag is PMC_VALUE_FLAGS_CHILDREN which speci-
            fies that the returned counts should be accumulated values for any
            exited child processes.

     pmc_accumulate(struct lwp *l_parent, struct lwp *l_exiting)
            Accumulates any counter data from the exiting process p_exiting
            into the counters for the parent process p_parent.

     pmc_alloc_kernel_counter(int ctr, struct pmc_counter_cfg *cfg)
            Allocates counter ctr for use by the kernel and configures it with
            cfg.

     pmc_free_kernel_counter(int ctr)
            Returns counter ctr to the available pool of counters that may be
            used by processes.

     pmc_start_profiling(int ctr, struct pmc_counter_cfg *cfg)
            Allocates counter ctr for use by the kernel for profiling and con-
            figures it with cfg.

     pmc_stop_profiling(int ctr)
            Stops profiling with counter ctr.

     PMC_ENABLED(struct lwp *l)
            Returns non-zero if the given process or the kernel is using the
            PMC at all.

SEE ALSO
     pmc(1), pmc_control(2), pmc_get_info(2)

HISTORY
     The pmc interface appeared in NetBSD 2.0.

AUTHORS
     The pmc interface was designed and implemented by Allen Briggs for Wasabi
     Systems, Inc.  Additional input on the pmc design was provided by Jason
     R. Thorpe.

NetBSD 6.1.3                     May 14, 2010                     NetBSD 6.1.3

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