1 files changed, 8 insertions, 0 deletions
diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index b468c33df6..02a7dafec3 100644
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -1739,6 +1739,13 @@ loop:
 }
 
 
+// NOTE: there is another implementation of this function in
+// Threads.c:performTryPutMVar().  Keep them in sync!  It was
+// measurably slower to call the C function from here (70% for a
+// tight loop doing tryPutMVar#).
+//
+// TODO: we could kill the duplication by making tryPutMVar# into an
+// inline primop that expands into a C call to performTryPutMVar().
 stg_tryPutMVarzh ( P_ mvar, /* :: MVar a */
                    P_ val,  /* :: a */ )
 {
@@ -1812,6 +1819,7 @@ loop:
     return (1);
 }
 
+
 stg_readMVarzh ( P_ mvar, /* :: MVar a */ )
 {
     W_ val, info, tso, q;