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diff --git a/docs/users_guide/runtime_control.xml b/docs/users_guide/runtime_control.xml
index e89f340..e0dd420 100644
--- a/docs/users_guide/runtime_control.xml
+++ b/docs/users_guide/runtime_control.xml
@@ -108,6 +108,14 @@
the or options.
However, setting is required in order to
increase the resolution of the time profiler.
+
+ Using a value of zero disables the RTS clock
+ completely, and has the effect of disabling timers that
+ depend on it: the context switch timer and the heap profiling
+ timer. Context switches will still happen, but
+ deterministically and at a rate much faster than normal.
+ Disabling the interval timer is useful for debugging, because
+ it eliminates a source of non-determinism at runtime.
@@ -122,6 +130,35 @@
own signal handlers.
+
+
+
+ RTS
+ option
+
+
+ WARNING: this option is for working around memory
+ allocation problems only. Do not use unless GHCi fails
+ with a message like “failed to mmap() memory below 2Gb”. If you need to use this option to get GHCi working
+ on your machine, please file a bug.
+
+
+
+ On 64-bit machines, the RTS needs to allocate memory in the
+ low 2Gb of the address space. Support for this across
+ different operating systems is patchy, and sometimes fails.
+ This option is there to give the RTS a hint about where it
+ should be able to allocate memory in the low 2Gb of the
+ address space. For example, +RTS -xm20000000
+ -RTS would hint that the RTS should allocate
+ starting at the 0.5Gb mark. The default is to use the OS's
+ built-in support for allocating memory in the low 2Gb if
+ available (e.g. mmap
+ with MAP_32BIT on Linux), or
+ otherwise -xm40000000.
+
+
+
@@ -260,6 +297,43 @@
+
+ threads
+ RTS option
+
+
+ [Default: 1] [new in GHC 6.10] Set the number
+ of threads to use for garbage collection. This option is
+ only accepted when the program was linked with the
+ option; see .
+
+ The garbage collector is able to work in parallel when
+ given more than one OS thread. Experiments have shown
+ that this 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.
+
+ This value is set automatically when the
+ option is used, so the only reason to
+ use would be if you wanted to use a
+ different number of threads for GC than for execution.
+ For example, if your program is strictly single-threaded
+ but you still want to benefit from parallel GC, then it
+ might make sense to use rather than
+ .
+
+
+
+ sizeRTS option
@@ -391,46 +465,258 @@
+
+ file
+ RTS option
+
- file
+ fileRTS option
- file
+ fileRTS option
- Write modest () or verbose
- () garbage-collector statistics into file
- file. The default
- file is
- program.stat. The
- filestderr
- is treated specially, with the output really being sent to
- stderr.
-
- This option is useful for watching how the storage
- manager adjusts the heap size based on the current amount of
- live data.
-
-
+ These options produce runtime-system statistics, such
+ as the amount of time spent executing the program and in the
+ garbage collector, the amount of memory allocated, the
+ maximum size of the heap, and so on. The three
+ variants give different levels of detail:
+ produces a single line of output in the
+ same format as GHC's option,
+ produces a more detailed summary at the
+ end of the program, and additionally
+ produces information about each and every garbage
+ collection.
+
+ The output is placed in
+ file. If
+ file is omitted, then the output
+ is sent to stderr.
+
+
+ If you use the -t flag then, when your
+ program finishes, you will see something like this:
+
+
+
+<<ghc: 36169392 bytes, 69 GCs, 603392/1065272 avg/max bytes residency (2 samples), 3M in use, 0.00 INIT (0.00 elapsed), 0.02 MUT (0.02 elapsed), 0.07 GC (0.07 elapsed) :ghc>>
+
+
+
+ This tells you:
+
+
+
+
+
+ The total bytes allocated by the program. This may be less
+ than the peak memory use, as some may be freed.
+
+
+
+
+ The total number of garbage collections that occurred.
+
+
+
+
+ The average and maximum space used by your program.
+ This is only checked during major garbage collections, so it
+ is only an approximation; the number of samples tells you how
+ many times it is checked.
+
+
+
+
+ The peak memory the RTS has allocated from the OS.
+
+
+
+
+ The amount of CPU time and elapsed wall clock time while
+ initialising the runtime system (INIT), running the program
+ itself (MUT, the mutator), and garbage collecting (GC).
+
+
+
+
+
+ If you use the -s flag then, when your
+ program finishes, you will see something like this (the exact
+ details will vary depending on what sort of RTS you have, e.g.
+ you will only see profiling data if your RTS is compiled for
+ profiling):
+
+
+
+ 36,169,392 bytes allocated in the heap
+ 4,057,632 bytes copied during GC
+ 1,065,272 bytes maximum residency (2 sample(s))
+ 54,312 bytes maximum slop
+ 3 MB total memory in use (0 MB lost due to fragmentation)
+
+ Generation 0: 67 collections, 0 parallel, 0.04s, 0.03s elapsed
+ Generation 1: 2 collections, 0 parallel, 0.03s, 0.04s elapsed
+
+ SPARKS: 359207 (557 converted, 149591 pruned)
+
+ INIT time 0.00s ( 0.00s elapsed)
+ MUT time 0.01s ( 0.02s elapsed)
+ GC time 0.07s ( 0.07s elapsed)
+ EXIT time 0.00s ( 0.00s elapsed)
+ Total time 0.08s ( 0.09s elapsed)
+
+ %GC time 89.5% (75.3% elapsed)
+
+ Alloc rate 4,520,608,923 bytes per MUT second
+
+ Productivity 10.5% of total user, 9.1% of total elapsed
+
+
+
+
+
+ The "bytes allocated in the heap" is the total bytes allocated
+ by the program. This may be less than the peak memory use, as
+ some may be freed.
+
+
+
+
+ GHC uses a copying garbage collector. "bytes copied during GC"
+ tells you how many bytes it had to copy during garbage collection.
+
+
+
+
+ The maximum space actually used by your program is the
+ "bytes maximum residency" figure. This is only checked during
+ major garbage collections, so it is only an approximation;
+ the number of samples tells you how many times it is checked.
+
+
+
+
+ The "bytes maximum slop" tells you the most space that is ever
+ wasted due to the way GHC packs data into so-called "megablocks".
+
+
+
+
+ The "total memory in use" tells you the peak memory the RTS has
+ allocated from the OS.
+
+
+
+
+ Next there is information about the garbage collections done.
+ For each generation it says how many garbage collections were
+ done, how many of those collections used multiple threads,
+ the total CPU time used for garbage collecting that generation,
+ and the total wall clock time elapsed while garbage collecting
+ that generation.
+
+
+
+ The SPARKS statistic refers to the
+ use of Control.Parallel.par and related
+ functionality in the program. Each spark represents a call
+ to par; a spark is "converted" when it is
+ executed in parallel; and a spark is "pruned" when it is
+ found to be already evaluated and is discarded from the pool
+ by the garbage collector. Any remaining sparks are
+ discarded at the end of execution, so "converted" plus
+ "pruned" does not necessarily add up to the total.
+
+
+
+ Next there is the CPU time and wall clock time elapsedm broken
+ down by what the runtiem system was doing at the time.
+ INIT is the runtime system initialisation.
+ MUT is the mutator time, i.e. the time spent actually running
+ your code.
+ GC is the time spent doing garbage collection.
+ RP is the time spent doing retainer profiling.
+ PROF is the time spent doing other profiling.
+ EXIT is the runtime system shutdown time.
+ And finally, Total is, of course, the total.
+
+
+ %GC time tells you what percentage GC is of Total.
+ "Alloc rate" tells you the "bytes allocated in the heap" divided
+ by the MUT CPU time.
+ "Productivity" tells you what percentage of the Total CPU and wall
+ clock elapsed times are spent in the mutator (MUT).
+
+
+
+
+
+ The -S flag, as well as giving the same
+ output as the -s flag, prints information
+ about each GC as it happens:
+
+
+
+ Alloc Copied Live GC GC TOT TOT Page Flts
+ bytes bytes bytes user elap user elap
+ 528496 47728 141512 0.01 0.02 0.02 0.02 0 0 (Gen: 1)
+[...]
+ 524944 175944 1726384 0.00 0.00 0.08 0.11 0 0 (Gen: 0)
+
+
+
+ For each garbage collection, we print:
+
+
+
+
+
+ How many bytes we allocated this garbage collection.
+
+
+
+
+ How many bytes we copied this garbage collection.
+
+
+
+
+ How many bytes are currently live.
+
+
+
+
+ How long this garbage collection took (CPU time and elapsed
+ wall clock time).
+
+
+
+
+ How long the program has been running (CPU time and elapsed
+ wall clock time).
+
+
+
+
+ How many page faults occured this garbage collection.
+
+
+
+
+ How many page faults occured since the end of the last garbage
+ collection.
+
+
+
+
+ Which generation is being garbage collected.
+
+
+
-
-
-
- RTS option
-
-
- Write a one-line GC stats summary after running the
- program. This output is in the same format as that produced
- by the option.
-
- As with , the default
- file is
- program.stat. The
- filestderr
- is treated specially, with the output really being sent to
- stderr.
@@ -438,14 +724,46 @@
- RTS options for profiling and parallelism
+ RTS options for concurrency and parallelism
- The RTS options related to profiling are described in , those for concurrency in
+ The RTS options related to concurrency are described in
, and those for parallelism in
.
+
+ RTS options for profiling
+
+ Most profiling runtime options are only available when you
+ compile your program for profiling (see
+ , and
+ for the runtime options).
+ However, there is one profiling option that is available
+ for ordinary non-profiled executables:
+
+
+
+
+
+ RTS
+ option
+
+
+ Generates a basic heap profile, in the
+ file prog.hp.
+ To produce the heap profile graph,
+ use hp2ps (see ). The basic heap profile is broken down by data
+ constructor, with other types of closures (functions, thunks,
+ etc.) grouped into broad categories
+ (e.g. FUN, THUNK). To
+ get a more detailed profile, use the full profiling
+ support ().
+
+
+
+
+
RTS options for hackers, debuggers, and over-interested
souls
@@ -653,6 +971,29 @@ char *ghc_rts_opts = "-H128m -K1m";
ghc/compiler/parser/hschooks.c in a GHC
source tree.
+
+
+ Getting information about the RTS
+
+ RTS
+
+ It is possible to ask the RTS to give some information about
+ itself. To do this, use the flag, e.g.
+
+$ ./a.out +RTS --info
+ [("GHC RTS", "Yes")
+ ,("GHC version", "6.7")
+ ,("RTS way", "rts_p")
+ ,("Host platform", "x86_64-unknown-linux")
+ ,("Build platform", "x86_64-unknown-linux")
+ ,("Target platform", "x86_64-unknown-linux")
+ ,("Compiler unregisterised", "NO")
+ ,("Tables next to code", "YES")
+ ]
+
+ The information is formatted such that it can be read as a
+ of type [(String, String)].
+