If the issue is that the GC implementation in Oracle's JVMs typically has a sequential bottleneck in it with default parameters, then yes, Amdahl's law is striking *for that GC implementation*.
For problems that are embarassingly parallel (little or no communication or shared memory between threads), there is no law of the universe that says that GC must have a sequential bottleneck in it. A GC better tuned for such problems could be developed, and perhaps already has. Lee, did you ever get a trial for Azul's Zing JVM to see if its GC was any better in this regard? Andy On Sun, Apr 28, 2013 at 8:47 AM, Gary Trakhman <gary.trakh...@gmail.com>wrote: > Amdahl strikes again! I knew this lunch was too tasty to be free. > > I just thought of another analogy. When I think of something highly > concurrent and scalable on the JVM, I think of web request handlers, which > effectively use no memory-sharing for domain-specific work, at all, unless > there is some in-memory application state, but in general they shift the > problem to a database. When the bookkeeping overhead doesn't dominate, > they appear to be highly concurrent. > > Shared-memory a wall of abstraction, multi-core cpus don't work this way > at the bottom level, so writing programs this way can only go so far. > > > > > On Sun, Apr 28, 2013 at 11:22 AM, Manuel Paccagnella < > manuel.paccagne...@gmail.com> wrote: > >> Ok, for everyone that is interested: >> this<http://www.meetup.com/Functional-Programming-Connoisseurs/messages/boards/thread/30946382>thread >> on meetup clarified things a bit for me and probably it's a good >> summary on the specific case that Lee found. >> >> >> Il giorno domenica 28 aprile 2013 17:07:04 UTC+2, Lee ha scritto: >> >>> >>> On Apr 28, 2013, at 10:57 AM, Manuel Paccagnella wrote: >>> > >>> > This is an interesting perspective. Are you saying that currently >>> Clojure doesn't offer adequate tools to take full advantage of parallel >>> execution on multi-core machines? >>> >>> I am speaking only from my own experience, and only relative to my own >>> case. But I've been unable to get reasonable speedups for my system, which >>> I think should be an excellent candidate for multi-core speedups. And while >>> I'm not an expert on JVM/Clojure performance I solicited and received >>> advice from people on this list who I think are, and I'm still unable to >>> get reasonable speedups -- maybe a couple of X but maybe not even that, on >>> machines with core-counts up to 48. It may have to do with the kinds of >>> tasks I'm running (lots of sequence manipulation and memory consumption, >>> etc.), but for whatever reason I am still unable to get Clojure's >>> oft-touted multi-core benefits. >>> >>> -Lee >>> >>> -- >> -- >> 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 >> --- >> You received this message because you are subscribed to the Google Groups >> "Clojure" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> >> > > -- > -- > 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 > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
