Make profiling work with multiple capabilities (+RTS -N)

This means that both time and heap profiling work for parallel
programs.  Main internal changes:

  - CCCS is no longer a global variable; it is now another
    pseudo-register in the StgRegTable struct.  Thus every
    Capability has its own CCCS.

  - There is a new built-in CCS called "IDLE", which records ticks for
    Capabilities in the idle state.  If you profile a single-threaded
    program with +RTS -N2, you'll see about 50% of time in "IDLE".

  - There is appropriate locking in rts/Profiling.c to protect the
    shared cost-centre-stack data structures.

This patch does enough to get it working, I have cut one big corner:
the cost-centre-stack data structure is still shared amongst all
Capabilities, which means that multiple Capabilities will race when
updating the "allocations" and "entries" fields of a CCS.  Not only
does this give unpredictable results, but it runs very slowly due to
cache line bouncing.

It is strongly recommended that you use -fno-prof-count-entries to
disable the "entries" count when profiling parallel programs. (I shall
add a note to this effect to the docs).

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/codeGen/CgCase.lhs b/compiler/codeGen/CgCase.lhs
index e4fe386043..a36621bdaf 100644
--- a/compiler/codeGen/CgCase.lhs
+++ b/compiler/codeGen/CgCase.lhs
@@ -670,6 +670,6 @@ restoreCurrentCostCentre Nothing     _freeit = nopC
 restoreCurrentCostCentre (Just slot) freeit
  = do 	{ sp_rel <- getSpRelOffset slot
 	; whenC freeit (freeStackSlots [slot])
-	; stmtC (CmmStore curCCSAddr (CmmLoad sp_rel bWord)) }
+        ; stmtC (storeCurCCS (CmmLoad sp_rel bWord)) }
 \end{code}