X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2FThreads.c;h=f6b1bac1a78d55696154937ff59498f170c7f9bd;hb=3d7ffacd15ac7f44393a2b0186972c8903a1b643;hp=7344134a7d5a0d54e6a1d6bc60aa66c7c8277842;hpb=83d563cb9ede0ba792836e529b1e2929db926355;p=ghc-hetmet.git

diff --git a/rts/Threads.c b/rts/Threads.c
index 7344134..f6b1bac 100644
--- a/rts/Threads.c
+++ b/rts/Threads.c
@@ -163,9 +163,11 @@ removeThreadFromQueue (Capability *cap, StgTSO **queue, StgTSO *tso)
 	if (t == tso) {
 	    if (prev) {
 		setTSOLink(cap,prev,t->_link);
+                t->_link = END_TSO_QUEUE;
                 return rtsFalse;
 	    } else {
 		*queue = t->_link;
+                t->_link = END_TSO_QUEUE;
                 return rtsTrue;
 	    }
 	}
@@ -190,7 +192,8 @@ removeThreadFromDeQueue (Capability *cap,
 		*head = t->_link;
                 flag = rtsTrue;
 	    }
-	    if (*tail == tso) {
+            t->_link = END_TSO_QUEUE;
+            if (*tail == tso) {
 		if (prev) {
 		    *tail = prev;
 		} else {
@@ -284,6 +287,19 @@ unblock:
     // we'll block again.
     tso->why_blocked = NotBlocked;
     appendToRunQueue(cap,tso);
+
+    // We used to set the context switch flag here, which would
+    // trigger a context switch a short time in the future (at the end
+    // of the current nursery block).  The idea is that we have just
+    // woken up a thread, so we may need to load-balance and migrate
+    // threads to other CPUs.  On the other hand, setting the context
+    // switch flag here unfairly penalises the current thread by
+    // yielding its time slice too early.
+    //
+    // The synthetic benchmark nofib/smp/chan can be used to show the
+    // difference quite clearly.
+
+    // cap->context_switch = 1;
 }
 
 /* ----------------------------------------------------------------------------