<Term><Option>-C[<us>]</Option>:</Term>
<ListItem>
<Para>
-<IndexTerm><Primary>-C<us> RTS option</Primary></IndexTerm>
-Sets the context switch interval to <Literal><us></Literal> microseconds. A context
-switch will occur at the next heap allocation after the timer expires.
-With <Option>-C0</Option> or <Option>-C</Option>, context switches will occur as often as
-possible (at every heap allocation). By default, context switches
-occur every 10 milliseconds. Note that many interval timers are only
-capable of 10 millisecond granularity, so the default setting may be
-the finest granularity possible, short of a context switch at every
-heap allocation.
-</Para>
-
-<Para>
-[NOTE: this option currently has no effect (version 4.00). Context
-switches happen when the current heap block is full, i.e. every 4k of
-allocation].
+<IndexTerm><Primary>-C<us> RTS option</Primary></IndexTerm> Sets
+the context switch interval to <Literal><s></Literal> seconds.
+A context switch will occur at the next heap block allocation after
+the timer expires (a heap block allocation occurs every 4k of
+allocation). With <Option>-C0</Option> or <Option>-C</Option>,
+context switches will occur as often as possible (at every heap block
+allocation). By default, context switches occur every 20ms
+milliseconds. Note that GHC's internal timer ticks every 20ms, and
+the context switch timer is always a multiple of this timer, so 20ms
+is the maximum granularity available for timed context switches.
</Para>
</ListItem>
</VarListEntry>