X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fusing.xml;h=b2ac5012c1a08bb46689d7a807e849ad768a1335;hb=0db68e1cf9b83d2d18ba427ec28712de4c9a043f;hp=ef62d59118345da1cf8fd766f36401354a4d5bef;hpb=0f5e104c36b1dc3d8deeec5fef3d65e7b3a1b5ad;p=ghc-hetmet.git diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml index ef62d59..b2ac501 100644 --- a/docs/users_guide/using.xml +++ b/docs/users_guide/using.xml @@ -841,11 +841,13 @@ ghc -c Foo.hs of warnings which are generally likely to indicate bugs in your program. These are: , - , + , , , - , and - . The following flags are + , + , and + . The following + flags are simple ways to select standard “packages” of warnings: @@ -917,15 +919,16 @@ ghc -c Foo.hs - : + : - + + warnings deprecations - Causes a warning to be emitted when a deprecated - function or type is used. Entities can be marked as - deprecated using a pragma, see . + Causes a warning to be emitted when a + module, function or type with a WARNING or DEPRECATED pragma + is used. See for more + details on the pragmas. This option is on by default. @@ -945,6 +948,30 @@ ghc -c Foo.hs + : + + + + Causes a warning to be emitted for foreign imports of + the following form: + +foreign import "f" f :: FunPtr t + + on the grounds that it probably should be + +foreign import "&f" f :: FunPtr t + + The first form declares that `f` is a (pure) C + function that takes no arguments and returns a pointer to a + C function with type `t`, whereas the second form declares + that `f` itself is a C function with type `t`. The first + declaration is usually a mistake, and one that is hard to + debug because it results in a crash, hence this + warning. + + + + : @@ -1152,7 +1179,8 @@ f foo = foo { x = 6 } The trouble with orphans is that GHC must pro-actively read the interface files for all orphan modules, just in case their instances or rules play a role, whether or not the module's interface would otherwise - be of any use. Other things being equal, avoid orphan modules. + be of any use. See for details. + @@ -1738,7 +1766,7 @@ f "2" = 2 parallelism. - Options to enable SMP parallelism + Options for SMP parallelism In order to make use of multiple CPUs, your program must be linked with the option (see RTS option Use x simultaneous threads when running the program. Normally x - should be chosen to match the number of CPU cores on the machine. - There is no means (currently) by which this value may vary after - the program has started. - - For example, on a dual-core machine we would probably use + should be chosen to match the number of CPU cores on the + machineWhether hyperthreading cores should be counted or not is an + open question; please feel free to experiment and let us know what + results you find.. For example, + on a dual-core machine we would probably use +RTS -N2 -RTS. - Whether hyperthreading cores should be counted or not is an - open question; please feel free to experiment and let us know what - results you find. + Setting also has the effect of + setting (the number of OS threads to + use for garbage collection) to the same value. + + There is no means (currently) by which this value + may vary after the program has started. + + The following options affect the way the runtime schedules + threads on CPUs: + + + + + RTS + option + + Disable automatic migration for load balancing. + Normally the runtime will automatically try to schedule + threads across the available CPUs to make use of idle + CPUs; this option disables that behaviour. It is probably + only of use if you are explicitly scheduling threads onto + CPUs with GHC.Conc.forkOnIO. + + + + + RTS + option + + Migrate a thread to the current CPU when it is woken + up. Normally when a thread is woken up after being + blocked it will be scheduled on the CPU it was running on + last; this option allows the thread to immediately migrate + to the CPU that unblocked it. + + The rationale for allowing this eager migration is + that it tends to move threads that are communicating with + each other onto the same CPU; however there are + pathalogical situations where it turns out to be a poor + strategy. Depending on the communication pattern in your + program, it may or may not be a good idea. + + + Hints for using SMP parallelism - Add the -sstderr RTS option when + Add the -s RTS option when running the program to see timing stats, which will help to tell you whether your program got faster by using more CPUs or not. If the user time is greater than @@ -1837,7 +1906,7 @@ statements or clauses. GHC can dump its optimized intermediate code (said to be in “Core” format) to a file as a side-effect of compilation. Non-GHC back-end tools can read and process Core files; these files have the suffix - .hcr. The Core format is described in + .hcr. The Core format is described in An External Representation for the GHC Core Language, and sample tools for manipulating Core files (in Haskell) are in the GHC source distribution