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in reply to Matching lines in 2+ GB logfiles.

Just my first thought; so instead of

while ( $window =~ m/\w{3}\s{1,2}\d{1,2}.*$re.*\n/oigc ) {
you could try
while ( $window =~ m/\w\w\w\s\s?\d\d?.*$re.*\n/iogc ) {

\w\w\w should run faster than \w{3}, same with \d\d? instead of \d{1,2}

Edit: and same with \s\s? vs. \s{1,2}. The direction should be clear.

Edit2: Maybe precompiling the regex with the qr// Operator might give another speedup.
By the way, I can't remember that /c Modifier, what is it for?