From a078252410f284229e5f2440e7b8a9b32a6cfd33 Mon Sep 17 00:00:00 2001 From: Simon Marlow Date: Thu, 15 Jan 2009 09:39:22 +0000 Subject: [PATCH] document -feager-blackholing --- docs/users_guide/flags.xml | 7 ++++++ docs/users_guide/using.xml | 51 ++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 54 insertions(+), 4 deletions(-) diff --git a/docs/users_guide/flags.xml b/docs/users_guide/flags.xml index aa84b81..05794df 100644 --- a/docs/users_guide/flags.xml +++ b/docs/users_guide/flags.xml @@ -1429,6 +1429,13 @@ static - + + + + Turn on eager blackholing + dynamic + - + diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml index ce7ef76..439fb58 100644 --- a/docs/users_guide/using.xml +++ b/docs/users_guide/using.xml @@ -1765,15 +1765,58 @@ f "2" = 2 linkend="lang-parallel" /> we describe the language features that affect parallelism. - - Options for SMP parallelism + + Compile-time options for SMP parallelism In order to make use of multiple CPUs, your program must be linked with the option (see ). Then, to run a program on multiple - CPUs, use the RTS option: + linkend="options-linker" />). Additionally, the following + compiler options affect parallelism: + + + + + + Blackholing is the act of marking a thunk (lazy + computuation) as being under evaluation. It is useful for + three reasons: firstly it lets us detect certain kinds of + infinite loop (the NonTermination + exception), secondly it avoids certain kinds of space + leak, and thirdly it avoids repeating a computation in a + parallel program, because we can tell when a computation + is already in progress. + + + The option causes + each thunk to be blackholed as soon as evaluation begins. + The default is "lazy blackholing", whereby thunks are only + marked as being under evaluation when a thread is paused + for some reason. Lazy blackholing is typically more + efficient (by 1-2% or so), because most thunks don't + need to be blackholed. However, eager blackholing can + avoid more repeated computation in a parallel program, and + this often turns out to be important for parallelism. + + + + We recommend compiling any code that is intended to be run + in parallel with the + flag. + + + + + + + + RTS options for SMP parallelism + + To run a program on multiple CPUs, use the + RTS option: + + -- 1.7.10.4