Andy, I just thought I'd mention that for 80 cents you can rent an hour on an 8-core EC2 machine with 7GB of RAM. We use EC2 a lot for such things at work. It may be an easy way for you to accomplish your goals. http://aws.amazon.com/ec2/instance-types/
Chad Harrington chad.harring...@gmail.com On Sat, Aug 8, 2009 at 4:27 AM, Andy Fingerhut < andy_finger...@alum.wustl.edu> wrote: > > Johann, if you are still following this thread, could you try running > this Clojure program on your 8 core machine? > > > http://github.com/jafingerhut/clojure-benchmarks/blob/3e45bd8f6c3eba47f982a0f6083493a9f076d0e9/misc/pmap-testing.clj > > These first set of parameters below will do 8 jobs sequentially, each > doing 10^10 (inc c)'s, where c is a double primitive. The second will > do the 8 jobs in parallel, hopefully finishing about 8 times faster on > your machine: > > java -cp <your_class_path> clojure.main pmap-testing.clj double2 8 > 10000000000 1 > java -cp <your_class_path> clojure.main pmap-testing.clj double2 8 > 10000000000 8 > > If you replace double2 with double1, it should reproduce your initial > test case with (inc 0.1) in the inner loop -- the one that started > this thread about why there wasn't much speedup. > > > I created some Clojure and Java functions that are as similar as I > know how to make them, but frankly I don't really know whether my JVM > implementation (Apple's java 1.6.0_13) is using 'new Double', or a > cache as mentioned by John Harrop earlier in this discussion, in its > implementation of Double.valueOf(double). I've found that the > performance is very similar to a Java program that uses 'new Double' > explicitly in its inner loop. > > In the results linked below, the 'sequential' runs are for calling the > function named twice in a row, whereas the 'parallel' runs are for > having two parallel threads, on my 2 core machine, each of which calls > the named function once. The total amount of computation in each case > should be the same, so you'd hope that the parallel case would finish > in about half the time, with about the same amount of total CPU time > being utilized. > > That isn't what happens for the Java code with 'new Double' (called > NewDoubleTest), or for the Clojure code that has (inc 0.1) and calls > Double.valueOf(double) down in its implementation (called spin- > double1). The parallel case only saves about 14% of the elapsed time > with 2 cores, and takes about 50% more total CPU time. > > The more typical code that takes a single double value, initializes > it, and then adds 1 to it each time through the inner loop (Java > DoubleTest, Clojure spin-double2), is significantly faster than the > versions mentioned above. Plus they exhibit the expected speedup from > using 2 cores instead of 1. > > > http://github.com/jafingerhut/clojure-benchmarks/blob/3e45bd8f6c3eba47f982a0f6083493a9f076d0e9/misc/RESULTS > > I'm not sure how to determine why calling 'new Double' each time > through NewDoubleTest's inner loop causes 2 threads to perform not > much better than 1. The best possible explanation I've heard is from > Nicolas Oury -- perhaps we are measuring the bandwidth from cache to > main memory, not raw computational ability of the processor cores. > > Andy > > > --~--~---------~--~----~------------~-------~--~----~ 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 Note that posts from new members are moderated - please be patient with your first post. 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 -~----------~----~----~----~------~----~------~--~---
