perfmonctl(2)		       System Calls Manual		   perfmonctl(2)

NAME
     perfmonctl - interface to IA-64 performance monitoring unit

SYNOPSIS
     #include <syscall.h>
     #include <perfmon.h>

     long perfmonctl(int narg;
		     int fd, int cmd, void arg[narg], int narg);

     Note: There is no glibc wrapper for this system call; see HISTORY.

DESCRIPTION
     The  IA-64-specific  perfmonctl()	system call provides an interface to the
     PMU (performance monitoring unit).	 The PMU consists  of  PMD  (performance
     monitoring	 data) registers and PMC (performance monitoring control) regis-
     ters, which gather hardware statistics.

     perfmonctl() applies the operation cmd to the input arguments specified  by
     arg.   The	 number of arguments is defined by narg.  The fd argument speci-
     fies the perfmon context to operate on.

     Supported values for cmd are:

     PFM_CREATE_CONTEXT
	    perfmonctl(int fd, PFM_CREATE_CONTEXT, pfarg_context_t *ctxt, 1);
	    Set up a context.

	    The fd parameter is ignored.  A new perfmon context	 is  created  as
	    specified	in   ctxt   and	 its  file  descriptor	is  returned  in
	    ctxt->ctx_fd.

	    The file descriptor can be used in subsequent calls to  perfmonctl()
	    and	 can  be used to read event notifications (type pfm_msg_t) using
	    read(2).  The file descriptor is pollable using select(2),	poll(2),
	    and epoll(7).

	    The	 context  can  be  destroyed by calling close(2) on the file de-
	    scriptor.

     PFM_WRITE_PMCS
	    perfmonctl(int fd, PFM_WRITE_PMCS, pfarg_reg_t *pmcs, n);
	    Set PMC registers.

     PFM_WRITE_PMDS
	    perfmonctl(int fd, PFM_WRITE_PMDS, pfarg_reg_t *pmds, n);
	    Set PMD registers.

     PFM_READ_PMDS
	    perfmonctl(int fd, PFM_READ_PMDS, pfarg_reg_t *pmds, n);
	    Read PMD registers.

     PFM_START
	    perfmonctl(int fd, PFM_START, NULL, 0);
	    Start monitoring.

     PFM_STOP
	    perfmonctl(int fd, PFM_STOP, NULL, 0);
	    Stop monitoring.

     PFM_LOAD_CONTEXT
	    perfmonctl(int fd, PFM_LOAD_CONTEXT, pfarg_load_t *largs, 1);
	    Attach the context to a thread.

     PFM_UNLOAD_CONTEXT
	    perfmonctl(int fd, PFM_UNLOAD_CONTEXT, NULL, 0);
	    Detach the context from a thread.

     PFM_RESTART
	    perfmonctl(int fd, PFM_RESTART, NULL, 0);
	    Restart monitoring after receiving an overflow notification.

     PFM_GET_FEATURES
	    perfmonctl(int fd, PFM_GET_FEATURES, pfarg_features_t *arg, 1);

     PFM_DEBUG
	    perfmonctl(int fd, PFM_DEBUG, val, 0);
	    If val is nonzero, enable debugging mode, otherwise disable.

     PFM_GET_PMC_RESET_VAL
	    perfmonctl(int fd, PFM_GET_PMC_RESET_VAL, pfarg_reg_t *req, n);
	    Reset PMC registers to default values.

RETURN VALUE
     perfmonctl() returns zero when the operation is successful.  On  error,  -1
     is returned and errno is set to indicate the error.

STANDARDS
     Linux on IA-64.

HISTORY
     Linux 2.4.	 Removed in Linux 5.10.

     This  system  call was broken for many years, and was ultimately removed in
     Linux 5.10.

     glibc does not provide a wrapper for this system call; on kernels where  it
     exists, call it using syscall(2).

SEE ALSO
     gprof(1)

     The perfmon2 interface specification

Linux man-pages 6.18		   2026-02-22			   perfmonctl(2)