.\" $NetBSD: pmc.9,v 1.14 2016/06/01 08:17:47 wiz Exp $
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.\" Written by Allen Briggs for Wasabi Systems, Inc.
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.Dd June 1, 2016
.Dt PMC 9
.Os
.Sh NAME
.Nm pmc ,
.Nm pmc_get_num_counters ,
.Nm pmc_get_counter_type ,
.Nm pmc_save_context ,
.Nm pmc_restore_context ,
.Nm pmc_enable_counter ,
.Nm pmc_disable_counter ,
.Nm pmc_counter_isrunning ,
.Nm pmc_counter_isconfigured ,
.Nm pmc_configure_counter ,
.Nm pmc_get_counter_value ,
.Nm pmc_accumulate ,
.Nm pmc_alloc_kernel_counter ,
.Nm pmc_free_kernel_counter ,
.Nm pmc_start_profiling ,
.Nm pmc_stop_profiling ,
.Nm PMC_ENABLED
.Nd Hardware Performance Monitoring Interface
.Sh SYNOPSIS
.In sys/pmc.h
.Ft int
.Fn pmc_get_num_counters "void"
.Ft int
.Fn pmc_get_counter_type "int ctr"
.Ft void
.Fn pmc_save_context "struct lwp *l"
.Ft void
.Fn pmc_restore_context "struct lwp *l"
.Ft int
.Fn pmc_enable_counter "struct lwp *l" "int ctr"
.Ft int
.Fn pmc_disable_counter "struct lwp *l" "int ctr"
.Ft int
.Fn pmc_counter_isrunning "struct lwp *l" "int ctr"
.Ft int
.Fn pmc_counter_isconfigured "struct lwp *l" "int ctr"
.Ft int
.Fn pmc_configure_counter "struct lwp *l" "int ctr" \
"struct pmc_counter_cfg *cfg"
.Ft int
.Fn pmc_get_counter_value "struct lwp *l" "int ctr" "int flags" \
"uint64_t *pval"
.Ft int
.Fn pmc_accumulate "struct lwp *l_parent" "struct lwp *l_exiting"
.Ft int
.Fn pmc_alloc_kernel_counter "int ctr" "struct pmc_counter_cfg *cfg"
.Ft int
.Fn pmc_free_kernel_counter "int ctr"
.Ft int
.Fn pmc_start_profiling "int ctr" "struct pmc_counter_cfg *cfg"
.Ft int
.Fn pmc_stop_profiling "int ctr"
.Ft int
.Fn PMC_ENABLED "struct lwp *l"
.Sh 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.
.Pp
The
.Nm
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.
.Sh IMPLEMENTATION NOTES
All function calls in this interface may be defined as
.Xr cpp 1
macros.
If any function is not implemented as a macro, its prototype must be
defined by the port-specific header
.In machine/pmc.h .
.Pp
Counters are numbered from 0 to
.Dv N\-1
where
.Dv N
is the number of counters available on the system
(see
.Fn pmc_get_num_counters
below).
.Pp
Upon a process fork, implementations must
.Bl -bullet
.It
Zero performance counters for the new process, and
.It
Inherit any enabled performance counters.
.El
.Sh DATA TYPES
Each implementation must specify two new types:
.Bl -tag -width pmc_evid_t
.It Fa pmc_evid_t
An integer type which can contain the event IDs for a given processor.
.It Fa pmc_ctr_t
An integer type defining the value which may be contained in a given
counter register.
.El
.Pp
Counters are configured with the
.Fa struct pmc_counter_cfg .
This structure is defined as
.Bd -literal
struct pmc_counter_cfg {
	pmc_evid_t	event_id;
	pmc_ctr_t	reset_value;
	uint32_t	flags;
};
.Ed
.Pp
.Fa flags
are currently unused.
.Sh FUNCTIONS
.Bl -tag -width width
.It Fn pmc_get_num_counters "void"
Returns the number of counters present on the current system.
Valid values for
.Fa ctr
in the interface entry points below are from zero to one less than the
return value from this function.
.It Fn pmc_get_counter_type "int ctr"
Returns an implementation-dependent type describing the specified counter.
If
.Fa 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.
.It Fn pmc_save_context "struct lwp *l"
Saves the PMC context for the current process.
This is called just before
.Xr cpu_switchto 9 .
If there is kernel PMC state, it must be maintained across this call.
.It Fn pmc_restore_context "struct lwp *l"
Restores the PMC context for the current process.
This is called just after
.Xr cpu_switchto 9
returns.
If there is kernel PMC state, it must be maintained across this call.
.It Fn pmc_enable_counter "struct lwp *l" "int ctr"
Enables counter
.Fa ctr
for the specified process.
The counter should have already been configured with a call to
.Fn pmc_configure_counter .
This starts the counter running if it is not already started and enables
any interrupts, as appropriate.
.It Fn pmc_disable_counter "struct lwp *l" "int ctr"
Disables counter
.Fa ctr
for the specified process.
This stops the counter from running, and disables any interrupts,
as appropriate.
.It Fn 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.
.It Fn 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.
.It Fn pmc_configure_counter "struct lwp *l" "int ctr" \
"struct pmc_counter_cfg *cfg"
Configures counter
.Fa ctr
according to the configuration information stored in
.Fa cfg .
.It Fn pmc_get_counter_value "struct lwp *l" "int ctr" "int flags" \
"uint64_t *pval"
Returns the value of counter
.Fa ctr
in the space pointed to by
.Fa pval .
The only recognized flag is
.Fa PMC_VALUE_FLAGS_CHILDREN
which specifies that the returned counts should be accumulated values
for any exited child processes.
.It Fn pmc_accumulate "struct lwp *l_parent" "struct lwp *l_exiting"
Accumulates any counter data from the exiting process
.Fa p_exiting
into the counters for the parent process
.Fa p_parent .
.It Fn pmc_alloc_kernel_counter "int ctr" "struct pmc_counter_cfg *cfg"
Allocates counter
.Fa ctr
for use by the kernel and configures it with
.Fa cfg .
.It Fn pmc_free_kernel_counter "int ctr"
Returns counter
.Fa ctr
to the available pool of counters that may be used by processes.
.It Fn pmc_start_profiling "int ctr" "struct pmc_counter_cfg *cfg"
Allocates counter
.Fa ctr
for use by the kernel for profiling and configures it with
.Fa cfg .
.It Fn pmc_stop_profiling "int ctr"
Stops profiling with counter
.Fa ctr .
.It Fn PMC_ENABLED "struct lwp *l"
Returns non-zero if the given process or the kernel is using the PMC at all.
.El
.Sh SEE ALSO
.Xr pmc 1 ,
.Xr pmc_control 2 ,
.Xr pmc_get_info 2
.Sh HISTORY
The
.Nm
interface appeared in
.Nx 2.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
interface was designed and implemented by
.An Allen Briggs
for Wasabi Systems, Inc.
Additional input on the
.Nm
design was provided by
.An Jason R. Thorpe .