NAME

       s390_runtime_instr - enable/disable s390 CPU run-time instrumentation

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <asm/runtime_instr.h> /* Definition of S390_* constants */
       #include <sys/syscall.h>       /* Definition of SYS_* constants */
       #include <unistd.h>

       int syscall(SYS_s390_runtime_instr, int command, int signum);

       Note:  glibc  provides  no  wrapper  for  s390_runtime_instr(),  necessitating  the use of
       syscall(2).

DESCRIPTION

       The s390_runtime_instr() system call starts or stops CPU run-time instrumentation for  the
       calling thread.

       The    command   argument   controls   whether   run-time   instrumentation   is   started
       (S390_RUNTIME_INSTR_START, 1) or stopped  (S390_RUNTIME_INSTR_STOP,  2)  for  the  calling
       thread.

       The signum argument specifies the number of a real-time signal.  This argument was used to
       specify a  signal  number  that  should  be  delivered  to  the  thread  if  the  run-time
       instrumentation  buffer  was  full or if the run-time-instrumentation-halted interrupt had
       occurred.  This feature was never used, and in Linux 4.4  support  for  this  feature  was
       removed; thus, in current kernels, this argument is ignored.

RETURN VALUE

       On   success,   s390_runtime_instr()  returns  0  and  enables  the  thread  for  run-time
       instrumentation by assigning the thread a default run-time instrumentation control  block.
       The   caller  can  then  read  and  modify  the  control  block  and  start  the  run-time
       instrumentation.  On error, -1 is returned and errno is set to indicate the error.

ERRORS

       EINVAL The value specified in command is not a valid command.

       EINVAL The value specified in signum is not a real-time signal  number.   From  Linux  4.4
              onwards,  the  signum argument has no effect, so that an invalid signal number will
              not result in an error.

       ENOMEM Allocating memory for the run-time instrumentation control block failed.

       EOPNOTSUPP
              The run-time instrumentation facility is not available.

STANDARDS

       Linux on s390.

HISTORY

       Linux 3.7.  System z EC12.

NOTES

       The asm/runtime_instr.h header file is available since Linux 4.16.

       Starting with Linux 4.4, support for signalling was removed,  as  was  the  check  whether
       signum is a valid real-time signal.  For backwards compatibility with older kernels, it is
       recommended to pass a valid real-time signal number in signum and install  a  handler  for
       that signal.

SEE ALSO

       syscall(2), signal(7)