From d15cb49d6fe600090fac7c56805ee4b13f4aaa47 Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Thu, 6 Nov 2008 16:08:10 +0000
Subject: [PATCH] re-instate counting of sparks converted lost in patch "Run
 sparks in batches"

---
 rts/Capability.c |   19 ++++++++++++++++---
 rts/Capability.h |    4 ++--
 rts/PrimOps.cmm  |   10 ++--------
 3 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/rts/Capability.c b/rts/Capability.c
index ddb47b4..9b5d81d 100644
--- a/rts/Capability.c
+++ b/rts/Capability.c
@@ -55,7 +55,7 @@ globalWorkToDo (void)
 
 #if defined(THREADED_RTS)
 StgClosure *
-stealWork (Capability *cap)
+findSpark (Capability *cap)
 {
   /* use the normal Sparks.h interface (internally modified to enable
      concurrent stealing) 
@@ -66,12 +66,24 @@ stealWork (Capability *cap)
   rtsBool retry;
   nat i = 0;
 
+  // first try to get a spark from our own pool.
+  // We should be using reclaimSpark(), because it works without
+  // needing any atomic instructions:
+  //   spark = reclaimSpark(cap->sparks);
+  // However, measurements show that this makes at least one benchmark
+  // slower (prsa) and doesn't affect the others.
+  spark = tryStealSpark(cap);
+  if (spark != NULL) {
+      cap->sparks_converted++;
+      return spark;
+  }
+
+  if (n_capabilities == 1) { return NULL; } // makes no sense...
+
   debugTrace(DEBUG_sched,
 	     "cap %d: Trying to steal work from other capabilities", 
 	     cap->no);
 
-  if (n_capabilities == 1) { return NULL; } // makes no sense...
-
   do {
       retry = rtsFalse;
 
@@ -96,6 +108,7 @@ stealWork (Capability *cap)
               debugTrace(DEBUG_sched,
 		 "cap %d: Stole a spark from capability %d",
                          cap->no, robbed->no);
+              cap->sparks_converted++;
               return spark;
           }
           // otherwise: no success, try next one
diff --git a/rts/Capability.h b/rts/Capability.h
index 07b8838..db9e1e3 100644
--- a/rts/Capability.h
+++ b/rts/Capability.h
@@ -245,9 +245,9 @@ void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
 //
 rtsBool tryGrabCapability (Capability *cap, Task *task);
 
-// Try to steal a spark from other Capabilities
+// Try to find a spark to run
 //
-StgClosure *stealWork (Capability *cap);
+StgClosure *findSpark (Capability *cap);
 
 // True if any capabilities have sparks
 //
diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index 55ada8c..f63f20a 100644
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -2295,17 +2295,11 @@ getSparkzh_fast
 #ifndef THREADED_RTS
    RET_NP(0,ghczmprim_GHCziBool_False_closure);
 #else
-   (spark) = foreign "C" tryStealSpark(MyCapability());
+   (spark) = foreign "C" findSpark(MyCapability());
    if (spark != 0) {
       RET_NP(1,spark);
    } else {
-      (spark) = foreign "C" stealWork (MyCapability());
-      if (spark != 0) {
-         RET_NP(1,spark);
-      } else {
-         RET_NP(0,ghczmprim_GHCziBool_False_closure);
-
-      }
+      RET_NP(0,ghczmprim_GHCziBool_False_closure);
    }
 #endif
 }
-- 
1.7.10.4