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, 0 insertions, 6 deletions

diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c
index 3e3290dd3d..650c4f9a04 100644
--- a/rts/RtsFlags.c
+++ b/rts/RtsFlags.c
@@ -1147,12 +1147,6 @@ error = rtsTrue;
                       errorBelch("Using large values for -N is not allowed by default. Link with -rtsopts to allow full control.");
                       stg_exit(EXIT_FAILURE);
                     }
-#if defined(PROFILING)
-                    if (nNodes > 1) {
-                        errorBelch("bad option %s: only -N1 is supported with profiling", rts_argv[arg]);
-		      error = rtsTrue;
-                    }
-#endif
                     RtsFlags.ParFlags.nNodes = (nat)nNodes;
 		}
 		) break;