Oh yes. The code is essentially identical to that I posted in Re^3: How to split file for threading?, with a little additional timing code.

This is that slightly modified code, the output from the runs above and the graph:

#! perl -slw
use strict;
use Time::HiRes qw[ time ];
use threads;

sub worker {
    my( $filename, $target, $start, $end ) = @_;
    open my $fh, '<', $filename or die $!;

    seek $fh, $start, 0;
    <$fh> if $start > 0; ## discard first partial line

    my $count = 0;
    1+index( <$fh>, $target ) and ++$count while tell( $fh ) < $end;

    return $count;
}

my $start = time;
our $T //= 4;

my( $filename, $target ) = @ARGV;
my $fsize = -s $filename;
my $chunksize = int( $fsize / $T );
my @chunks = map{ $_ * $chunksize } 0 .. $T-1;
push @chunks, $fsize;

my @threads = map{
    threads->new( \&worker, $filename, $target, $chunks[ $_ ], $chunks
+[ $_+1 ] )
} 0 .. $T-1;

my $total = 0;
$total += $_->join for @threads;

print "Found $total '$target' lines";
printf "Took %.9f secs cpu(%s)\n", time()-$start, join ' ', times;

__END__
[20:39:41.83] C:\test>1131634.pl -T=1 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 207.819706917 secs cpu(162.296 15.906 0 0)
[20:43:09.82] C:\test>1131634.pl -T=2 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 169.678593159 secs cpu(164.203 18.968 0 0)
[20:46:00.25] C:\test>1131634.pl -T=3 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 156.497795820 secs cpu(164.375 18.656 0 0)
[20:48:37.34] C:\test>1131634.pl -T=4 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 127.086592913 secs cpu(161.843 19.546 0 0)
[20:50:45.04] C:\test>1131634.pl -T=5 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 115.240671158 secs cpu(161.89 19.109 0 0)
[20:52:40.87] C:\test>1131634.pl -T=6 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 129.716307163 secs cpu(161.781 21.859 0 0)
[20:54:51.19] C:\test>1131634.pl -T=7 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 167.007865906 secs cpu(162.328 22.171 0 0)
[20:57:38.78] C:\test>1131634.pl -T=8 s:\1GBx8.bin lAxc
Found 10 'lAxc' lines Took 179.142831087 secs cpu(164.171 25.546 0 0)


      210   ---
  E   200   ...                               165.0
  l   190   ...                               164.8
  a   180   ...                         ___   164.6
  p   170   ... ___  X                  ...   164.4    C
  s   160   ... .X.                 --- .X.   164.2    P
  e   150   ... ... ---             ... ...   164.0    U
  d   140   ... ... ...         ___ ... ...   163.8
      130   ... ... ...         ... ... ...   163.6    S
  s   120   ... ... ... ---     ... ... ...   163.4    e
  e   110   ... ... ... ... --- ... ... ...   163.2    c
  c   100   .X. ... ... ... ... ... ... ...   163.0    o
  o    90   ... ... ... ... ... ... ... ...   162.8    n
  n    80   ... ... ... ... ... ... ... ...   162.6    d
  d    70   ... ... ... ... ... ... .X. ...   162.4    s
  s    60   ... ... ... ... ... ... ... ...   162.2    .
  .    50   ... ... ... ... ... ... ... ...   162.0
       40   ... ... ... .X. .X. .X. ... ...   161.8
       30   ... ... ... ... ... ... ... ...   161.6
       20   ... ... ... ... ... ... ... ...   161.4
       10   ... ... ... ... ... ... ... ...   161.2
             1   2   3   4   5   6   7   8
               T   H   R   E   A   D   S
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