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diff --git a/docs/users_guide/runtime_control.xml b/docs/users_guide/runtime_control.xml
index 69e26bc..c482a28 100644
--- a/docs/users_guide/runtime_control.xml
+++ b/docs/users_guide/runtime_control.xml
@@ -298,51 +298,58 @@
-
- RTS
+
+ RTS
option
- [New in GHC 6.12.1] Disable the parallel GC.
- The parallel GC is turned on automatically when parallel
- execution is enabled with the option;
- this option is available to turn it off if
- necessary.
+ [New in GHC 6.12.1] [Default: 0]
+ Use parallel GC in
+ generation gen and higher.
+ Omitting gen turns off the
+ parallel GC completely, reverting to sequential GC.
- Experiments have shown that parallel GC usually
- results in a performance improvement given 3 cores or
- more; with 2 cores it may or may not be beneficial,
- depending on the workload. Bigger heaps work better with
- parallel GC, so set your value high (3
- or more times the maximum residency). Look at the timing
- stats with to see whether you're
- getting any benefit from parallel GC or not. If you find
- parallel GC is significantly slower
- (in elapsed time) than sequential GC, please report it as
- a bug.
-
- In GHC 6.10.1 it was possible to use a different
- number of threads for GC than for execution, because the GC
- used its own pool of threads. Now, the GC uses the same
- threads as the mutator (for executing the program).
+ The default parallel GC settings are usually suitable
+ for parallel programs (i.e. those
+ using par, Strategies, or with multiple
+ threads). However, it is sometimes beneficial to enable
+ the parallel GC for a single-threaded sequential program
+ too, especially if the program has a large amount of heap
+ data and GC is a significant fraction of runtime. To use
+ the parallel GC in a sequential program, enable the
+ parallel runtime with a suitable -N
+ option, and additionally it might be beneficial to
+ restrict parallel GC to the old generation
+ with -qg1.
-
- RTS
+
+ RTS
option
- [Default: 1] [New in GHC 6.12.1]
- Enable the parallel GC only in
- generation n and greater.
- Parallel GC is often not worthwhile for collections in
- generation 0 (the young generation), so it is enabled by
- default only for collections in generation 1 (and higher,
- if applicable).
+ [New in GHC 6.12.1] [Default: 1] Use
+ load-balancing in the parallel GC in
+ generation gen and higher.
+ Omitting gen disables
+ load-balancing entirely.
+
+
+ Load-balancing shares out the work of GC between the
+ available cores. This is a good idea when the heap is
+ large and we need to parallelise the GC work, however it
+ is also pessimal for the short young-generation
+ collections in a parallel program, because it can harm
+ locality by moving data from the cache of the CPU where is
+ it being used to the cache of another CPU. Hence the
+ default is to do load-balancing only in the
+ old-generation. In fact, for a parallel program it is
+ sometimes beneficial to disable load-balancing entirely
+ with -qb.
@@ -810,6 +817,92 @@
+
+ Tracing
+
+ tracing
+ events
+ eventlog files
+
+
+ When the program is linked with the
+ option (), runtime events can
+ be logged in two ways:
+
+
+
+
+
+ In binary format to a file for later analysis by a
+ variety of tools. One such tool
+ is ThreadScopeThreadScope,
+ which interprets the event log to produce a visual parallel
+ execution profile of the program.
+
+
+
+
+ As text to standard output, for debugging purposes.
+
+
+
+
+
+
+
+
+ RTS option
+
+
+
+ Log events in binary format to the
+ file program.eventlog,
+ where type indicates the type
+ of events to log. Currently there is only one type
+ supported: -ls, for scheduler events.
+
+
+
+ The format of the log file is described by the header
+ EventLogFormat.h that comes with
+ GHC, and it can be parsed in Haskell using
+ the ghc-events
+ library. To dump the contents of
+ a .eventlog file as text, use the
+ tool show-ghc-events that comes with
+ the ghc-events
+ package.
+
+
+
+
+
+
+
+ RTS option
+
+
+
+ Log events as text to standard output, instead of to
+ the .eventlog file.
+
+
+
+
+
+
+
+ The debugging
+ options also
+ generate events which are logged using the tracing framework.
+ By default those events are dumped as text to stdout
+ (
+ implies ), but they may instead be stored in
+ the binary eventlog file by using the
+ option.
+
+
+
RTS options for hackers, debuggers, and over-interested
souls
@@ -846,14 +939,28 @@
- num
+ x-DRTS option
- An RTS debugging flag; varying quantities of output
- depending on which bits are set in
- num. Only works if the RTS was
- compiled with the option.
+
+ An RTS debugging flag; only availble if the program was
+ linked with the option. Various
+ values of x are provided to
+ enable debug messages and additional runtime sanity checks
+ in different subsystems in the RTS, for
+ example +RTS -Ds -RTS enables debug
+ messages from the scheduler.
+ Use +RTS -? to find out which
+ debug flags are supported.
+
+
+
+ Debug messages will be sent to the binary event log file
+ instead of stdout if the option is
+ added. This might be useful for reducing the overhead of
+ debug tracing.
+
@@ -866,20 +973,13 @@
Produce “ticky-ticky” statistics at the
- end of the program run. The file
- business works just like on the RTS
- option (above).
-
- “Ticky-ticky” statistics are counts of
- various program actions (updates, enters, etc.) The program
- must have been compiled using
-
- (a.k.a. “ticky-ticky profiling”), and, for it to
- be really useful, linked with suitable system libraries.
- Not a trivial undertaking: consult the installation guide on
- how to set things up for easy “ticky-ticky”
- profiling. For more information, see .
+ end of the program run (only available if the program was
+ linked with ).
+ The file business works just like
+ on the RTS option, above.
+
+ For more information on ticky-ticky profiling, see
+ .