Make it possible to use +RTS -qn without -N

It's entirely reasonable to set +RTS -qn without setting -N, because the
program might later call setNumCapabilities.  If we disallow it, there's
no way to use -qn on programs that use setNumCapabilities.

2 files changed, 5 insertions, 8 deletions

diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c
index d86b154342..aeb2fe532f 100644
--- a/rts/RtsFlags.c
+++ b/rts/RtsFlags.c
@@ -1487,13 +1487,6 @@ static void normaliseRtsOpts (void)
             RtsFlags.ParFlags.parGcLoadBalancingGen = 1;
         }
     }
-
-#ifdef THREADED_RTS
-    if (RtsFlags.ParFlags.parGcThreads > RtsFlags.ParFlags.nCapabilities) {
-        errorBelch("GC threads (-qn) must be between 1 and the value of -N");
-        errorUsage();
-    }
-#endif
 }
 
 static void errorUsage (void)
diff --git a/rts/Schedule.c b/rts/Schedule.c
index 06db3fe81f..a44512b3cb 100644
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -1596,7 +1596,11 @@ scheduleDoGC (Capability **pcap, Task *task USED_IF_THREADS,
             // enabled_capabilities may change if requestSync() below fails and
             // we retry.
             if (gc_type == SYNC_GC_PAR && n_gc_threads > 0) {
-                need_idle = stg_max(0, enabled_capabilities - n_gc_threads);
+                if (n_gc_threads >= enabled_capabilities) {
+                    need_idle = 0;
+                } else {
+                    need_idle = enabled_capabilities - n_gc_threads;
+                }
             } else {
                 need_idle = 0;
             }