You may want to try to compile your regexps before the loop with something like :

  my $re1 = qr/3_prtnm_/;
  my $re2 = qr/2_tname_/;
  # ...
  while( <STDF> ) {
  
  # ...

      if( m/$re1/ ) {
         @tmp = split($re1);

         #...

      } elsif( m/$re2/ ) {
         @tmp = split($re2);

         #...

      }
   }
[download]

Another trick, if you have a few million lines to parse could be to rewrite the inside of the loop to something more like :

  my $re = qr/(3_prtnm_|2_prtnm_|2_mrslt_)/;

  # ...

  while( my $line = <STDF> ) {
    if( m/$re/ ) {
       my $sep = $1;
       my @tmp = split( /$sep/, $line );

       # ...

    }
  }
[download]

I'm not sure if the spedup would be noticable because of the varying split that should be benchmarked/optimized.

Have a look to http://www.stonehenge.com/merlyn/UnixReview/col28.html for regexp compilation.

One sure thing is that threading is hard to get right and in big loops there are generally many other possible optimizations to try before.