code and then links it with a non-trivial runtime system (RTS),
which handles storage management, profiling, etc.</para>
- <para>If you use the <literal>-rtsopts</literal> flag when linking,
+ <para>If you set the <literal>-rtsopts</literal> flag appropriately when linking,
you have some control over the behaviour of the RTS, by giving
special command-line arguments to your program.</para>
wraparound in the counters is <emphasis>your</emphasis>
fault!)</para>
- <para>Giving a <literal>+RTS -f</literal>
- <indexterm><primary><option>-f</option></primary><secondary>RTS option</secondary></indexterm> option
+ <para>Giving a <literal>+RTS -?</literal>
+ <indexterm><primary><option>-?</option></primary><secondary>RTS option</secondary></indexterm> option
will print out the RTS options actually available in your program
(which vary, depending on how you compiled).</para>
<indexterm><primary>environment variable</primary><secondary>for
setting RTS options</secondary></indexterm>
- <para>When the <literal>-rtsopts</literal> flag is used when linking,
+ <para>If the <literal>-rtsopts</literal> flag is set to
+ something other than <literal>none</literal> when linking,
RTS options are also taken from the environment variable
<envar>GHCRTS</envar><indexterm><primary><envar>GHCRTS</envar></primary>
</indexterm>. For example, to set the maximum heap size
<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>
<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>
<para>The hook <literal>ghc_rts_opts</literal><indexterm><primary><literal>ghc_rts_opts</literal></primary>
</indexterm>lets you set RTS
- options permanently for a given program. A common use for this is
+ options permanently for a given program, in the same way as the
+ newer <option>-with-rtsopts</option> linker option does. A common use for this is
to give your program a default heap and/or stack size that is
greater than the default. For example, to set <literal>-H128m
-K1m</literal>, place the following definition in a C source
projects / ghc-hetmet.git / blobdiff