Ah, good catch. :-) Edward
Excerpts from Iustin Pop's message of Sun Aug 14 14:25:02 -0400 2011: > On Sun, Aug 14, 2011 at 08:11:36PM +0200, Wishnu Prasetya wrote: > > Hi guys, > > > > I'm new in parallel programming with Haskell. I made a simple test > > program using that par combinator etc, and was a bit unhappy that it > > turns out to be slower than its sequential version. But firstly, I > > dont fully understand how to read the runtime report produced by GHC > > with -s option: > > > > SPARKS: 5 (5 converted, 0 pruned) > > > > INIT time 0.02s ( 0.01s elapsed) > > MUT time 3.46s ( 0.89s elapsed) > > GC time 5.49s ( 1.46s elapsed) > > EXIT time 0.00s ( 0.00s elapsed) > > Total time 8.97s ( 2.36s elapsed) > > > > As I understand it from the documentation, the left time-column is > > the CPU time, whereas the right one is elapses wall time. But how > > come that the wall time is less than the CPU time? Isn't wall time = > > user's perspective of time; so that is CPU time + IO + etc? > > Yes, but if you have multiple CPUs, then CPU time "accumulates" faster > than wall-clock time. > > Based on the above example, I guess you have or you run the program on 4 > cores (2.36 * 4 = 9.44, which means you got a very nice ~95% > efficiency). > > regards, > iustin > _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
