The following example displays the average time spent in the write() system call, organized by process name. This example uses the avg aggregating function, specifying the expression to average as the argument. The example averages the wall clock time spent in the system call and is saved in a file named writetime.d:

syscall::write:entry
{
  self->ts = timestamp;
}

syscall::write:return
/self->ts/
{
  @time[execname] = avg(timestamp - self->ts);
  self->ts = 0;
}

The following output shows the result of running this command, waiting a few seconds, and then pressing Ctrl-C:

# dtrace -s writetime.d 
dtrace: script 'writetime.d' matched 2 probes
^C

  gnome-session                                                  8260
  udisks-part-id                                                 9279
  gnome-terminal                                                 9378
  mozilla-xremote                                               10061
  abrt-handle-eve                                               13414
  vgdisplay                                                     13459
  avahi-daemon                                                  14043
  vgscan                                                        14190
  uptime                                                        14533
  lsof                                                          14903
  ip                                                            15075
  date                                                          15371
  ...
  ps                                                            91792
  sestatus                                                      98374
  pstree                                                       102566
  sysctl                                                       175427
  iptables                                                     192835
  udisks-daemon                                                250405
  python                                                       282544
  dbus-daemon                                                  491069
  lsblk                                                        582138
  Xorg                                                        2337328
  gconfd-2                                                   17880523
  cat                                                        59752284
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