diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/runtime_control.xml | 103 |
1 files changed, 87 insertions, 16 deletions
diff --git a/docs/users_guide/runtime_control.xml b/docs/users_guide/runtime_control.xml index 40409131cc..0e13f0e933 100644 --- a/docs/users_guide/runtime_control.xml +++ b/docs/users_guide/runtime_control.xml @@ -424,22 +424,88 @@ <varlistentry> <term> - <option>-k</option><replaceable>size</replaceable> + <option>-ki</option><replaceable>size</replaceable> <indexterm><primary><option>-k</option></primary><secondary>RTS option</secondary></indexterm> - <indexterm><primary>stack, minimum size</primary></indexterm> + <indexterm><primary>stack, initial size</primary></indexterm> </term> <listitem> - <para>[Default: 1k] Set the initial stack size for - new threads. Thread stacks (including the main thread's - stack) live on the heap, and grow as required. The default - value is good for concurrent applications with lots of small - threads; if your program doesn't fit this model then - increasing this option may help performance.</para> - - <para>The main thread is normally started with a slightly - larger heap to cut down on unnecessary stack growth while - the program is starting up.</para> - </listitem> + <para> + [Default: 1k] Set the initial stack size for new + threads. (Note: this flag used to be + simply <option>-k</option>, but was renamed + to <option>-ki</option> in GHC 7.2.1. The old name is + still accepted for backwards compatibility, but that may + be removed in a future version). + </para> + + <para> + Thread stacks (including the main thread's stack) live on + the heap. As the stack grows, new stack chunks are added + as required; if the stack shrinks again, these extra stack + chunks are reclaimed by the garbage collector. The + default initial stack size is deliberately small, in order + to keep the time and space overhead for thread creation to + a minimum, and to make it practical to spawn threads for + even tiny pieces of work. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <option>-kc</option><replaceable>size</replaceable> + <indexterm><primary><option>-kc</option></primary><secondary>RTS + option</secondary></indexterm> + <indexterm><primary>stack</primary><secondary>chunk size</secondary></indexterm> + </term> + <listitem> + <para> + [Default: 32k] Set the size of “stack + chunks”. When a thread's current stack overflows, a + new stack chunk is created and added to the thread's + stack, until the limit set by <option>-K</option> is + reached. + </para> + + <para> + The advantage of smaller stack chunks is that the garbage + collector can avoid traversing stack chunks if they are + known to be unmodified since the last collection, so + reducing the chunk size means that the garbage collector + can identify more stack as unmodified, and the GC overhead + might be reduced. On the other hand, making stack chunks + too small adds some overhead as there will be more + overflow/underflow between chunks. The default setting of + 32k appears to be a reasonable compromise in most cases. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <option>-kb</option><replaceable>size</replaceable> + <indexterm><primary><option>-kc</option></primary><secondary>RTS + option</secondary></indexterm> + <indexterm><primary>stack</primary><secondary>chunk buffer size</secondary></indexterm> + </term> + <listitem> + <para> + [Default: 1k] Sets the stack chunk buffer size. + When a stack chunk overflows and a new stack chunk is + created, some of the data from the previous stack chunk is + moved into the new chunk, to avoid an immediate underflow + and repeated overflow/underflow at the boundary. The + amount of stack moved is set by the <option>-kb</option> + option. + </para> + <para> + Note that to avoid wasting space, this value should + typically be less than 10% of the size of a stack + chunk (<option>-kc</option>), because in a chain of stack + chunks, each chunk will have a gap of unused space of this + size. + </para> + </listitem> </varlistentry> <varlistentry> @@ -451,9 +517,14 @@ <listitem> <para>[Default: 8M] Set the maximum stack size for an individual thread to <replaceable>size</replaceable> - bytes. This option is there purely to stop the program - eating up all the available memory in the machine if it gets - into an infinite loop.</para> + bytes. If the thread attempts to exceed this limit, it will + be send the <literal>StackOverflow</literal> exception. + </para> + <para> + This option is there mainly to stop the program eating up + all the available memory in the machine if it gets into an + infinite loop. + </para> </listitem> </varlistentry> |