From: Xavier Leroy <Xavier.Leroy@inria.fr> To: Jason Ganetsky <jason.ganetsky@gmail.com> Cc: caml-list@yquem.inria.fr Subject: Re: [Caml-list] Multiprocessor support in OCaml Date: Sun, 22 Apr 2007 12:30:01 +0200 Message-ID: <462B3929.9080608@inria.fr> (raw) In-Reply-To: <ab351c020704220042x6e139375wa97393247ccc4867@mail.gmail.com> > Anyway, I have recently written an OCaml thread pool implementation, on > top of the Thread and Event modules. I did this for the purpose of > exploiting an SMP system I have, and was a disappointed to read today > that OCaml doesn't support multiprocessor systems. You are correct that OCaml *threads* do not exploit multiprocessing. Basically, only one OCaml thread can run at a time. You can still get parallelism in several ways. First, external C libraries called from OCaml can run in parallel with OCaml code provided the OCaml/C interface for these libraries makes uses of the "blocking section" mechanism. Second, process-level parallelism works very well with programs written in message-passing style, using e.g. OcamlMPI or OCamlP3L. > I played around with it a little, and discovered that by liberally > calling Thread.yield, I do cajole my threads into running on multiple > processors. This is an illusion. Thread.yield gives more opportunities to the OS scheduler to reschedule a Caml thread on a different processor, but you're not gaining parallelism this way and you might actually lose performance (because of cache ping-pong effects and the like). - Xavier Leroy
next prev parent reply index Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2007-04-22 7:42 Jason Ganetsky 2007-04-22 8:44 ` [Caml-list] " Richard Jones 2007-04-22 10:30 ` Xavier Leroy [this message] 2007-04-22 11:55 ` Don Syme 2007-04-22 10:58 ` Erik de Castro Lopo 2007-04-22 13:29 ` Jon Harrop 2007-04-22 17:31 ` Zheng Li [not found] ` <ab351c020704221052v50ce66b6maec299889a2c1f1f@mail.gmail.com> 2007-04-22 17:52 ` [Caml-list] " Jason Ganetsky 2007-04-23 8:10 ` Richard Jones
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