December 20, 2005 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

```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.

### 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 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 NetBSD2.0.

### 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.