You didn't say what kind of filtering you're doing, but if it were me I'd slurp in 2 lines at a time instead of the normal 1. For example:

open (F, "log.txt") or die "Couldn't open: $!";

while (1) {
    my $line1 = <F>; # Get a line
    my $line2 = <F>; # Get another line

    last unless defined($line1); # bail if there's no data

    #... now you can filter what you want here,
    # match, print, push whatever. All the data you 
    # care about is in $line1 and $line2
}
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Gary Blackburn
Trained Killer

Edited: Cleaned up the code a bit