runtime: re-enable preemption

Update #543

I believe the runtime is strong enough now to reenable
preemption during the function prologue.
Assuming this is or can be made stable, it will be in Go 1.2.
More aggressive preemption is not planned for Go 1.2.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/11433045

diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 3ce281fc775a0cb4999c961c87b347e0bc9130f3..74e92a63faf216b9c008dd87c28f29775ad7a672 100644 (file)
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -2175,12 +2175,6 @@ preemptone(P *p)
        M *mp;
        G *gp;
 
-// Preemption requires more robust traceback routines.
-// For now, disable.
-// The if(1) silences a compiler warning about the rest of the
-// function being unreachable.
-if(1) return;
-
        mp = p->m;
        if(mp == nil || mp == m)
                return;