Curiously Parallel

Well, not really, but sort of.

Take this code from http://cgi.cse.unsw.edu.au/~dons/blog/2007/11/29



Now, compiling it with no optimization, I get the following:

ghc --make fib.hs
time ./fib
real 5m50.175s
user 5m48.994s
sys 0m0.737s

ghc --make fib.hs -O2
time ./fib
real 5m48.966s
user 5m48.374s
sys 0m0.460s

Now with this code:

ghc --make -O2 -threaded
time ./pfib (Note the lack of RTS switches)

real 2m33.192s
user 2m32.883s
sys 0m0.173s

time ./pfib +RTS -N2

real 1m44.426s
user 2m38.416s
sys 0m1.587s

time ./pfib +RTS -N6 (It's an 8-core i7.  Well, 8 thread?  Does it actually do hyperthreading? I don't know)

real 1m24.359s
user 3m16.734s
sys 0m12.852s

Now with the optimized code

ghc --make -O2 -threaded sfib.hs
time ./sfib

real 1m3.752s
user 1m3.613s
sys 0m0.097s

time ./sfib +RTS -N2

real 0m33.545s
user 1m4.122s
sys 0m0.343s

time ./sfib +RTS -N4

real 0m17.462s
user 1m3.783s
sys 0m0.450s

time ./sfib +RTS -N6

real 0m16.076s
user 1m23.578s
sys 0m0.773s

time ./sfib +RTS -N8

real 11m55.785s
user 79m21.816s
sys 0m5.523s

Heh, for the first time since I bought the machine I heard the internal fans spin up to jet engine speeds.

Hrm, according to wikipedia, the processor is 4x but the Linux kernel sees 8. So it's 4 cores + hyperthreading or something? To be honest, I really don't care. It's fast enough to keep me entertained for quite a while.