If you are on linux, try running iostat -mx 5 while your threaded non-threaded perl script is processing the input. It will show you where the time is being spent. If most of your time is being spent in %iowait rather than %user, then you need to do something to reduce IO to reduce execution time, and as the previous post said, threads will not help you if this is the case. 
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.05    0.00    0.10    0.05    0.00   99.80

Device:         rrqm/s   wrqm/s   r/s   w/s    rMB/s    wMB/s avgrq-sz
+ avgqu-sz   await  svctm  %util
hda               0.00     5.80  0.20  2.00     0.00     0.03    29.82
+     0.01    4.45   2.36   0.52

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In reply to Re^2: how to split huge file reading into multiple threads by onelesd
in thread how to split huge file reading into multiple threads by sagarika

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