only use mach kernel semaphores for actual contention.

running rob's powser p.go:

3.21u 2.58s 5.80r 	 6.out	# old
1.48u 0.05s 1.54r 	 6.out	# new

R=r
OCL=15748
CL=15750

diff --git a/src/runtime/rt1_amd64_darwin.c b/src/runtime/rt1_amd64_darwin.c
index 02f03cdf7207d76e720f9ee7c5eea4989817c51f..2456bd788877ec8022a641e5dbf6489d2e49ee68 100644 (file)
--- a/src/runtime/rt1_amd64_darwin.c
+++ b/src/runtime/rt1_amd64_darwin.c
@@ -262,7 +262,7 @@ xadd(uint32 volatile *val, int32 delta)
 // releases the lock by decrementing l->key, l->key will
 // be >0, so it will increment the semaphore to wake up
 // one of the others.  This is the same algorithm used
-// in Plan 9's user-space locks.
+// in Plan 9's user-level locks.
 //
 // Note that semaphores are never destroyed (the kernel
 // will clean up when the process exits).  We assume for now
@@ -287,6 +287,25 @@ unlock(Lock *l)
 }
 
 
+// User-level semaphore implementation:
+// try to do the operations in user space on u,
+// but when it's time to block, fall back on the kernel semaphore k.
+// This is the same algorithm used in Plan 9.
+void
+usemacquire(Usema *s)
+{
+       if((int32)xadd(&s->u, -1) < 0)
+               semacquire(s->k);
+}
+
+void
+usemrelease(Usema *s)
+{
+       if((int32)xadd(&s->u, 1) <= 0)
+               semrelease(s->k);
+}
+
+
 // Event notifications.
 void
 noteclear(Note *n)
@@ -297,19 +316,19 @@ noteclear(Note *n)
 void
 notesleep(Note *n)
 {
-       if(n->sema == 0)
-               initsema(&n->sema);
+       if(n->sema.k == 0)
+               initsema(&n->sema.k);
        while(!n->wakeup)
-               semacquire(n->sema);
+               usemacquire(&n->sema);
 }
 
 void
 notewakeup(Note *n)
 {
-       if(n->sema == 0)
-               initsema(&n->sema);
+       if(n->sema.k == 0)
+               initsema(&n->sema.k);
        n->wakeup = 1;
-       semrelease(n->sema);
+       usemrelease(&n->sema);
 }
 
 

diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index 3d439ca452479096b4d2ebc1309245da87df9513..411b6046bfa4f32c67cb67f057824a56f751455c 100644 (file)
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -43,6 +43,7 @@ typedef       struct  Alg             Alg;
 typedef        struct  Lock            Lock;
 typedef        union   Note    Note;
 typedef        struct  Mem             Mem;
+typedef        struct  Usema   Usema;
 
 /*
  * per cpu declaration
@@ -77,6 +78,11 @@ struct       Lock
        uint32  key;
        uint32  sema;   // for OS X
 };
+struct Usema
+{
+       uint32  u;
+       uint32  k;
+};
 union  Note
 {
        struct {        // Linux
@@ -84,7 +90,7 @@ union Note
        };
        struct {        // OS X
                int32   wakeup;
-               uint32  sema;
+               Usema   sema;
        };
 };
 struct String