PMC(9) | 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 mispredicted, and so forth. Some can interrupt the processor when a certain threshold has been reached. Some can count events in user space and kernel 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_switchto(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_switchto(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 specifies 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 configures 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.

May 14, 2010 | NetBSD 7.2