.\" $NetBSD: pmc_control.2,v 1.7 2005/10/31 11:34:16 wiz Exp $
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.Dd October 27, 2005
.Dt PMC_CONTROL 2
.Os
.Sh NAME
.Nm pmc_control ,
.Nm pmc_get_info
.Nd Hardware Performance Monitoring Interface
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/pmc.h
.Ft int
.Fn pmc_control "int ctr" "int op" "void *argp"
.Ft int
.Fn pmc_get_info "int ctr" "int op" "void *argp"
.Sh DESCRIPTION
.Fn pmc_get_info
returns the number of counters in the system or information on a specified
counter
.Fa ctr .
The possible values for
.Fa op
are:
.Bl -tag -width width
.It Dv PMC_INFO_NCOUNTERS
When querying the number of counters in the system,
.Fa ctr
is ignored and
.Fa argp
is of type
.Ft int * .
Upon return, the integer pointed to by
.Fa argp
will contain the number of counters that are available in the system.
.It Dv PMC_INFO_CPUCTR_TYPE
When querying the type of a counter in the system,
.Fa ctr
refers to the counter being queried, and
.Fa argp
is of type
.Ft int * .
Upon return, the integer pointed to by
.Fa argp
will contain the implementation-dependent type of the specified counter.
.Pp
If
.Fa ctr
is \-1, the integer pointed to by
.Fa argp
will contain the machine-dependent type
describing the CPU or counter configuration.
.It Dv PMC_INFO_COUNTER_VALUE
When querying the value of a counter in the system,
.Fa ctr
refers to the counter being queried, and
.Fa argp
is of type
.Ft uint64_t * .
Upon return, the 64-bit integer pointed to by
.Fa argp
will contain the value of the specified counter.
.It Dv PMC_INFO_ACCUMULATED_COUNTER_VALUE
When querying the value of a counter in the system,
.Fa ctr
refers to the counter being queried, and
.Fa argp
is of type
.Ft uint64_t * .
Upon return, the 64-bit integer pointed to by
.Fa argp
will contain the sum of the accumulated values of specified counter in
all exited subprocesses of the current process.
.El
.Pp
.Fn pmc_control
manipulates the specified counter
.Fa ctr
in one of several fashions.
The
.Fa op
parameter determines the action taken by the kernel and also the interpretation of the
.Fa argp
parameter.
The possible values for
.Fa op
are:
.Bl -tag -width width
.It Dv PMC_OP_START
Starts the specified
.Fa ctr
running.
It must be preceded by a call with
.Dv PMC_OP_CONFIGURE .
.Fa argp
is ignored in this case and may be
.Dv NULL .
.It Dv PMC_OP_STOP
Stops the specified
.Fa ctr
from running.
.Fa argp
is ignored in this case and may be
.Dv NULL .
.It Dv PMC_OP_CONFIGURE
Configures the specified
.Fa ctr
prior to running.
.Fa argp
is a pointer to a
.Ft struct pmc_counter_cfg .
.Bd -literal
	struct pmc_counter_cfg {
		pmc_evid_t	event_id;
		pmc_ctr_t	reset_value;
		uint32_t	flags;
	};
.Ed
.Bl -tag -width width
.It Dv event_id
is the event ID to be counted.
.It Dv reset_value
is a value to which the counter should be reset on overflow (if supported
by the implementation).
This is most useful when profiling (see
.Dv PMC_OP_PROFSTART ,
below).
This value is defined to be the number of counter ticks before
the next overflow.
So, to get a profiling tick on every hundredth data cache miss, set the
.Dv event_id
to the proper value for
.Dq dcache-miss
and set
.Dv reset_value
to 100.
.It Dv flags
Currently unused.
.El
.It Dv PMC_OP_PROFSTART
Configures the specified
.Fa ctr
for use in profiling.
.Fa argp
is a pointer to a
.Ft struct pmc_counter_cfg
as in
.Dv PMC_OP_CONFIGURE ,
above.
This request allocates a kernel counter, which will fail if any
process is using the requested counter.
Not all implementations or counters may support this option.
.It Dv PMC_OP_PROFSTOP
Stops the specified
.Fa ctr
from being used for profiling.
.Fa argp
is ignored in this case and may be
.Dv NULL .
.El
.Sh RETURN VALUES
A return value of 0 indicates that the call succeeded.
Otherwise, \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
Among the possible error codes from
.Fn pmc_control
and
.Fn pmc_get_info
are
.Bl -tag -width Er
.It Bq Er EFAULT
The address specified for the
.Fa argp
is invalid.
.It Bq Er ENXIO
Specified counter is not yet configured.
.It Bq Er EINPROGRESS
.Dv PMC_OP_START
was passed for a counter that is already running.
.It Bq Er EINVAL
Specified counter was invalid.
.It Bq Er EBUSY
If the requested counter is already in use--either by the current process
or by the kernel.
.It Bq Er ENODEV
If and only if the specified counter event is not valid for the specified
counter when configuring a counter or starting profiling.
.It Bq Er ENOMEM
If the kernel is unable to allocate memory.
.El
.Sh SEE ALSO
.Xr pmc 1 ,
.Xr pmc 9
.Sh HISTORY
The
.Fn pmc_control
and
.Fn pmc_get_info
system calls appeared in
.Nx 2.0 .