Examples of coding and formatting events

Trace events can be used to time the execution of a program loop.

#include <sys/trcctl.h>
#include <sys/trcmacros.h>
#include <sys/trchkid.h>
char *ctl_file = "/dev/systrctl";
int ctlfd;
int i;
main()
{
  printf("configuring trace collection \n");
  if (trcstart("-ad")){
    perror("trcstart");
    exit(1);
  }

  printf("opening the trace device  \n");
  if((ctlfd = open(ctl_file,0))<0){
    perror(ctl_file);
    exit(1);
  }

  printf("turning  trace on \n");
  if(ioctl(ctlfd,TRCON,0)){
    perror("TRCON");
    exit(1);
  }

  for(i=1;i<11;i++){
    TRCHKL1T(HKWD_USER1,i);

    /* The code being measured goes here. The interval */
    /* between occurrences of HKWD_USER1 in the trace  */
    /* file is the total time for one iteration.       */
  }

  printf("turning trace off\n");
  if(ioctl(ctlfd,TRCSTOP,0)){
    perror("TRCOFF");
    exit(1);
  }

  printf("stopping the trace daemon \n");
  if (trcstop(0)){
    perror("trcstop");
    exit(1);
  }

  exit(0);
}

When you compile the sample program, you must link to the librts.a library as follows:

# xlc -O3 sample.c -o sample -l rts

HKWD_USER1 is event ID 010 hexadecimal (you can verify this by examining the /usr/include/sys/trchkid.h file). The report facility does not format the HKWD_USER1 event, unless rules are provided in the trace format file. The following example of a stanza for HKWD_USER1 could be used:

# User event HKWD_USER1 Formatting Rules Stanza
# An example that will format the event usage of the sample program
010 1.0 L=APPL "USER EVENT - HKWD_USER1" O2.0      \n \
               "The # of loop iterations =" U4     \n \
               "The elapsed time of the last loop = " \
                endtimer(0x010,0x010) starttimer(0x010,0x010)

When you enter the example stanza, do not modify the master format file /etc/trcfmt, but instead make a copy and keep it in your own directory (assume you name it mytrcfmt). When you run the sample program, the raw event data is captured in the default log file because no other log file was specified to the trcstart() subroutine. You can filter the output report to get only your events. To do this, run the trcrpt command as follows:

# trcrpt -d 010 -t mytrcfmt -O "exec=on" > sample.rpt

You can browse the sample.rpt file to see the result.