Cool! On Fri, Mar 6, 2009 at 5:35 PM, Dimiter malkia Stanev <mal...@gmail.com>wrote:
> > Thanks! Realized that a bit too late (Looked into the pmap source > code, but that's about it). > > I've split my job decision roughly 1000 x 1000 - now I'm getting 8 > times speedup, on 8 core machine: > > (reduce + > (pmap > (fn [_] > (reduce + > (map (fn [_] > (+ (pnpoly np xp yp 0.5 0.5) > (pnpoly np xp yp 0.5 1.5) > (pnpoly np xp yp -0.5 1.5) > (pnpoly np xp yp 0.75 2.25) > (pnpoly np xp yp 0.0 2.01) > (pnpoly np xp yp -0.5 2.5) > (pnpoly np xp yp -1.0 -0.5) > (pnpoly np xp yp -1.5 0.5) > (pnpoly np xp yp -2.25 -1.0) > (pnpoly np xp yp 0.5 -0.25) > (pnpoly np xp yp 0.5 -1.25) > (pnpoly np xp yp -0.5 -2.5))) > (range 0 1000)))) > (range 0 1000))) > > Clojure is reasonable :) > > Jeffrey Straszheim wrote: > > It is pretty common to get a slowdown when moving from map to pmap. It > just > > means that the thread scheduling overhead is greater than the gain from > > parallelizing the code. The behavior might be very different w/ larger > data > > sets, or w/ more CPU's. It is often best to leave parallelism as an > option > > to the client of your library. > > Are you using the latest build? pmap now uses Java futures and they run > in > > a cached thread pool. If so, try running the algorithm a few times and > see > > if it speeds up as the thread pool winds up. > > > > On Fri, Mar 6, 2009 at 1:31 PM, Dimiter malkia Stanev <mal...@gmail.com > >wrote: > > > > > > > > Hi guys, anyone has an insight into the problem I'm running into? > > > > > > On Mar 4, 2:27 am, "Dimiter \"malkia\" Stanev" <mal...@gmail.com> > > > wrote: > > > > Hi guys, > > > > > > > > In the example below, if map is replaced with pmap, it goes twice > > > > slower on my MBP (2 CPUs). > > > > > > > > I believe it's probably the (reduce + ...) causing it, but I can't > > > > explain it. > > > > > > > > Version with map: > > > > user> (time (pnpolytest)) > > > > "Elapsed time: 3903.533 msecs" > > > > 6000000 > > > > > > > > Version with pmap: > > > > user> (time (pnpolytest)) > > > > "Elapsed time: 7995.565 msecs" > > > > > > > > What I'm doing wrong here? > > > > > > > > (defn- pnpoly [npol #^floats xp #^floats yp x y] > > > > (let [npol (int npol) > > > > x (float x) > > > > y (float y)] > > > > (loop [r (int 0) > > > > i (int 0) > > > > xi (aget xp (dec npol)) > > > > yi (aget yp (dec npol))] > > > > (if (< i npol) > > > > (let [xj xi xi (aget xp i) > > > > yj yi yi (aget yp i)] > > > > (if (or (= (> yi y) (> yj y)) > > > > (>= x (+ xi (/ (* (- xj xi) > > > > (- y yi)) > > > > (- yj yi))))) > > > > (recur (bit-not r) (inc i) xi yi) > > > > (recur r (inc i) xi yi))) > > > > (- r))))) > > > > > > > > (defn pnpolytest [] > > > > (let [xp > > > > (float-array > > > > [+0.0 +1.0 +1.0 +0.0 +0.0 > > > > +1.0 -0.5 -1.0 -1.0 -2.0 > > > > -2.5 -2.0 -1.5 -0.5 +1.0 > > > > +1.0 +0.0 -0.5 -1.0 -0.5]) > > > > yp > > > > (float-array > > > > [+0.0 +0.0 +1.0 +1.0 +2.0 > > > > +3.0 +2.0 +3.0 0.0 -0.5 > > > > -1.0 -1.5 -2.0 -2.0 -1.5 > > > > -1.0 -0.5 -1.0 -1.0 -0.5]) > > > > npol 20] > > > > (reduce + > > > > ;; Replace the nex map with pmap, > > > > ;; and things slow down > > > > (map (fn [_] > > > > (+ (pnpoly npol xp yp 0.5 0.5) > > > > (pnpoly npol xp yp 0.5 1.5) > > > > (pnpoly npol xp yp -0.5 1.5) > > > > (pnpoly npol xp yp 0.75 2.25) > > > > (pnpoly npol xp yp 0.0 2.01) > > > > (pnpoly npol xp yp -0.5 2.5) > > > > (pnpoly npol xp yp -1.0 -0.5) > > > > (pnpoly npol xp yp -1.5 0.5) > > > > (pnpoly npol xp yp -2.25 -1.0) > > > > (pnpoly npol xp yp 0.5 -0.25) > > > > (pnpoly npol xp yp 0.5 -1.25) > > > > (pnpoly npol xp yp -0.5 -2.5))) > > > > (range 0 1000000))))) > > > > > > > > Thanks, > > > > Dimiter "malkia" Stanev > > > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
