Multiprocessing takes higher execution time

Nick Craig-Wood nick at
Wed Jan 7 17:31:15 CET 2009

Grant Edwards <invalid at invalid> wrote:
>  On 2009-01-07, Steve Holden <steve at> wrote:
> >> I use multiprocessing to compare more then one set of files.
> >> 
> >> For comparison each set of files (i.e. Old file1 Vs New file1)
> >> I create a process,
> >> 
> >> Process(target=compare, args=(oldFile, newFile)).start()
> >> 
> >> It takes 61 seconds execution time.
> >> 
> >> When I do the same comparison without implementing
> >> multiprocessing, it takes 52 seconds execution time.
> > My first suggestion would be: show us some code. We aren't
> > psychic, you know.
>  I am!
>  He's only got one processor, and he's just been bit by Amdahl's
>  law when P<1 and S<1.
>  There you have a perfectly "psychic" answer: an educated guess
>  camoflaged in plausible-sounding but mostly-bullshit buzzwords.
>  A better psychic would have avoided making that one falsifiable
>  statement (he's only got one processor).


My guess would be that the job is IO bound rather than CPU bound, but
that is covered by Amdahl's Law too where P is approx 0, N

Being IO bound explains why it takes longer with multiprocessing - it
causes more disk seeks to run an IO bound algorithm in parallel than
running it sequentially.

Nick Craig-Wood <nick at> --

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