Add a write barrier for TVAR closures

This improves GC performance when there are a lot of TVars in the
heap.  For instance, a TChan with a lot of elements causes a massive
GC drag without this patch.

There's more to do - several other STM closure types don't have write
barriers, so GC performance when there are a lot of threads blocked on
STM isn't great.  But fixing the problem for TVar is a good start.

2 files changed, 21 insertions, 19 deletions

diff --git a/includes/rts/storage/ClosureTypes.h b/includes/rts/storage/ClosureTypes.h
index 4e3b1e6a72..d878e965ee 100644
--- a/includes/rts/storage/ClosureTypes.h
+++ b/includes/rts/storage/ClosureTypes.h
@@ -61,23 +61,24 @@
 #define BLACKHOLE	        40
 #define MVAR_CLEAN	        41
 #define MVAR_DIRTY	        42
-#define ARR_WORDS	        43
-#define MUT_ARR_PTRS_CLEAN      44
-#define MUT_ARR_PTRS_DIRTY      45
-#define MUT_ARR_PTRS_FROZEN0    46
-#define MUT_ARR_PTRS_FROZEN     47
-#define MUT_VAR_CLEAN	        48
-#define MUT_VAR_DIRTY           49
-#define WEAK		        50
-#define PRIM		        51
-#define MUT_PRIM                52
-#define TSO		        53
-#define STACK                   54
-#define TREC_CHUNK              55
-#define ATOMICALLY_FRAME        56
-#define CATCH_RETRY_FRAME       57
-#define CATCH_STM_FRAME         58
-#define WHITEHOLE               59
-#define N_CLOSURE_TYPES         60
+#define TVAR                    43
+#define ARR_WORDS               44
+#define MUT_ARR_PTRS_CLEAN      45
+#define MUT_ARR_PTRS_DIRTY      46
+#define MUT_ARR_PTRS_FROZEN0    47
+#define MUT_ARR_PTRS_FROZEN     48
+#define MUT_VAR_CLEAN	        49
+#define MUT_VAR_DIRTY           50
+#define WEAK		        51
+#define PRIM		        52
+#define MUT_PRIM                53
+#define TSO		        54
+#define STACK                   55
+#define TREC_CHUNK              56
+#define ATOMICALLY_FRAME        57
+#define CATCH_RETRY_FRAME       58
+#define CATCH_STM_FRAME         59
+#define WHITEHOLE               60
+#define N_CLOSURE_TYPES         61
 
 #endif /* RTS_STORAGE_CLOSURETYPES_H */
diff --git a/includes/stg/MiscClosures.h b/includes/stg/MiscClosures.h
index af96563e53..61e6b0994f 100644
--- a/includes/stg/MiscClosures.h
+++ b/includes/stg/MiscClosures.h
@@ -101,6 +101,8 @@ RTS_ENTRY(stg_DEAD_WEAK);
 RTS_ENTRY(stg_STABLE_NAME);
 RTS_ENTRY(stg_MVAR_CLEAN);
 RTS_ENTRY(stg_MVAR_DIRTY);
+RTS_ENTRY(stg_TVAR_CLEAN);
+RTS_ENTRY(stg_TVAR_DIRTY);
 RTS_ENTRY(stg_TSO);
 RTS_ENTRY(stg_STACK);
 RTS_ENTRY(stg_ARR_WORDS);
@@ -130,7 +132,6 @@ RTS_ENTRY(stg_atomically);
 RTS_ENTRY(stg_TVAR_WATCH_QUEUE);
 RTS_ENTRY(stg_INVARIANT_CHECK_QUEUE);
 RTS_ENTRY(stg_ATOMIC_INVARIANT);
-RTS_ENTRY(stg_TVAR);
 RTS_ENTRY(stg_TREC_CHUNK);
 RTS_ENTRY(stg_TREC_HEADER);
 RTS_ENTRY(stg_END_STM_WATCH_QUEUE);