On Mon, Mar 23, 2009 at 2:21 PM, Michael van der Gulik <mike...@gmail.com>wrote:
> > > On Mon, Mar 23, 2009 at 12:34 PM, Igor Stasenko <siguc...@gmail.com>wrote: > >> >> Now consider the overhead of creating a fork vs the actual useful code >> which is running within a block. >> I presume, this code will run 10x times slower on a single core >> processor, comparing to one w/o forks. >> So, you will need to have 10 cores to match the computation time with >> single core processor. >> >> I think its not wise to introduce parallelism on such low levels (in >> Concurrent.Collections.Array>>withIndexDo:). Its like hammering nails >> with microscope :) >> >> That's why i'm saying its too good to be true. >> Introducing parallelism at such low levels will be a waste. I leaning >> toward island model. This is a middle point between no sharing, like >> in Hydra and sharing everything, like in what you proposing. >> > > 10 times slower? Sounds like a made-up number to me... > > " Using 101 threads: " > c := ConcurrentArray new: 1000001. > Time millisecondsToRun: [c withIndexDo: [ :each :i | c at: i put: i > asString. ]]. > 5711 > 5626 > 6074 > > " Using 11 threads: " > c := ConcurrentArray new: 1000001. > Time millisecondsToRun: [c withIndexDo: [ :each :i | c at: i put: i > asString. ]]. > 3086 > 3406 > 3256 > > " Using 1 thread: " > d := Array new: 1000001. > Time millisecondsToRun: [d withIndexDo: [ :each :i | d at: i put: i > asString]]. > 2426 > 2610 > 2599 > > My implementation is 1/2 to 1/3 the speed of the single-threaded Array. If > the blocks did more work, then the overhead would be lower and some benefit > would be gained from using multiple cores. > > I don't have a good idea of where the overhead is going - maybe it's being > lost in the block copying that is needed to work around Squeak's > deficiencies? Or maybe it's waiting for the scheduler to do its stuff? > > Implementation attached, MIT license if you're picky. > > I just tried it on VisualWorks as well. I removed the block copying and renamed the method to "keysDo:" (I never thought of an array like that before... keys and values). d := Array new: 1000001. Time millisecondsToRun: [d keysDo: [ :i | d at: i put: i printString]]. 1180 982 1008 " Using 101 threads " c := ConcurrentArray new: 1000001. Time millisecondsToRun: [c keysDo: [ :i | c at: i put: i printString. ]]. 1072 1120 962 At this stage, I'm suspicous about the results :-). Gulik. -- http://gulik.pbwiki.com/
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