X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fruntime_control.xml;h=3170f094d3045f649e8893b245aa020453fc14d0;hb=c6e9a86f03efb4fdef5ed10fcb93b64439fdec60;hp=5039526c756a8307ed2dcbcd2496d3b3a593b84c;hpb=816b587f0057113ce9667f1f643d828d7abe2079;p=ghc-hetmet.git
diff --git a/docs/users_guide/runtime_control.xml b/docs/users_guide/runtime_control.xml
index 5039526..3170f09 100644
--- a/docs/users_guide/runtime_control.xml
+++ b/docs/users_guide/runtime_control.xml
@@ -130,6 +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.
+
+
+
@@ -269,38 +298,52 @@
- threads
- RTS option
+
+ 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
- .
+ [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.
+
+ 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).
+
+
+
+
+
+
+ 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).
+
@@ -448,6 +491,10 @@
fileRTS option
+
+
+ RTS option
+ These options produce runtime-system statistics, such
as the amount of time spent executing the program and in the
@@ -514,6 +561,27 @@
+ You can also get this in a more future-proof, machine readable
+ format, with -t --machine-readable:
+
+
+
+ [("bytes allocated", "36169392")
+ ,("num_GCs", "69")
+ ,("average_bytes_used", "603392")
+ ,("max_bytes_used", "1065272")
+ ,("num_byte_usage_samples", "2")
+ ,("peak_megabytes_allocated", "3")
+ ,("init_cpu_seconds", "0.00")
+ ,("init_wall_seconds", "0.00")
+ ,("mutator_cpu_seconds", "0.02")
+ ,("mutator_wall_seconds", "0.02")
+ ,("GC_cpu_seconds", "0.07")
+ ,("GC_wall_seconds", "0.07")
+ ]
+
+
+
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.