reverting semaphore lock changes from sources (r41ccd6d221da, rb28756e5ba29)

semaphore locks have much higher overhead than initially presented
in the "Semaphores in Plan9" paper. until the reason for it has been
found out i will revert the changes.

3 files changed, 30 insertions, 84 deletions

diff --git a/sys/src/ape/lib/ap/power/atom.s b/sys/src/ape/lib/ap/power/atom.s
deleted file mode 100644
index b387300df..000000000
--- a/sys/src/ape/lib/ap/power/atom.s
+++ /dev/null
@@ -1,63 +0,0 @@
-TEXT	_xinc(SB),$0	/* void _xinc(long *); */
-TEXT	ainc(SB),$0	/* long ainc(long *); */
-	MOVW	R3, R4
-xincloop:
-	LWAR	(R4), R3
-	ADD	$1, R3
-	DCBT	(R4)				/* fix 405 errata cpu_210 */
-	STWCCC	R3, (R4)
-	BNE	xincloop
-	RETURN
-
-TEXT	_xdec(SB),$0	/* long _xdec(long *); */
-TEXT	adec(SB),$0	/* long adec(long *); */
-	MOVW	R3, R4
-xdecloop:
-	LWAR	(R4), R3
-	ADD	$-1, R3
-	DCBT	(R4)				/* fix 405 errata cpu_210 */
-	STWCCC	R3, (R4)
-	BNE	xdecloop
-	RETURN
-
-TEXT	loadlink(SB), $0
-
-	LWAR	(R3), R3
-	RETURN
-
-TEXT	storecond(SB), $0
-
-	MOVW	val+4(FP), R4
-	DCBT	(R3)				/* fix 405 errata cpu_210 */
-	STWCCC	R4, (R3)
-	BNE	storecondfail
-	MOVW	$1, R3
-	RETURN
-storecondfail:
-	MOVW	$0, R3
-	RETURN
-
-/*
- * int cas(uint *p, int ov, int nv);
- * int casp(void **p, void *ov, void *nv);
- */
-
-TEXT	cas+0(SB),0,$0
-TEXT	casp+0(SB),0,$0
-	MOVW	ov+4(FP),R4
-	MOVW	nv+8(FP),R8
-	LWAR	(R3),R5
-	CMP	R5,R4
-	BNE	fail
-	DCBT	(R3)				/* fix 405 errata cpu_210 */
-	STWCCC	R8,(R3)
-	BNE	fail1
-	MOVW	$1,R3
-	RETURN
-fail:
-	DCBT	(R3)				/* fix 405 errata cpu_210 */
-	STWCCC	R5,(R3)	/* give up exclusive access */
-fail1:
-	MOVW	R0,R3
-	RETURN
-	END
diff --git a/sys/src/ape/lib/ap/power/lock.c b/sys/src/ape/lib/ap/power/lock.c
index 65a65df7b..0d17c34d5 100644
--- a/sys/src/ape/lib/ap/power/lock.c
+++ b/sys/src/ape/lib/ap/power/lock.c
@@ -3,33 +3,43 @@
 #define _LOCK_EXTENSION
 #include <lock.h>
 
+int	tas(int*);
+
 void
-lock(Lock *l)
+lock(Lock *lk)
 {
-	if(ainc(&l->key) == 1)
-		return;	/* changed from 0 -> 1: we hold lock */
-	/* otherwise wait in kernel */
-	while(_SEMACQUIRE(&l->sem, 1) < 0){
-		/* interrupted; try again */
+	int i;
+
+	/* once fast */
+	if(!tas(&lk->val))
+		return;
+	/* a thousand times pretty fast */
+	for(i=0; i<1000; i++){
+		if(!tas(&lk->val))
+			return;
+		_SLEEP(0);
 	}
+	/* now nice and slow */
+	for(i=0; i<1000; i++){
+		if(!tas(&lk->val))
+			return;
+		_SLEEP(100);
+	}
+	/* take your time */
+	while(tas(&lk->val))
+		_SLEEP(1000);
 }
 
-void
-unlock(Lock *l)
+int
+canlock(Lock *lk)
 {
-	if(adec(&l->key) == 0)
-		return;	/* changed from 1 -> 0: no contention */
-	_SEMRELEASE(&l->sem, 1);
+	if(tas(&lk->val))
+		return 0;
+	return 1;
 }
 
-int
-canlock(Lock *l)
+void
+unlock(Lock *lk)
 {
-	if(ainc(&l->key) == 1)
-		return 1;	/* changed from 0 -> 1: success */
-	/* Undo increment (but don't miss wakeup) */
-	if(adec(&l->key) == 0)
-		return 0;	/* changed from 1 -> 0: no contention */
-	_SEMRELEASE(&l->sem, 1);
-	return 0;
+	lk->val = 0;
 }
diff --git a/sys/src/ape/lib/ap/power/mkfile b/sys/src/ape/lib/ap/power/mkfile
index ab4b35df6..cc546cd84 100644
--- a/sys/src/ape/lib/ap/power/mkfile
+++ b/sys/src/ape/lib/ap/power/mkfile
@@ -2,7 +2,6 @@ APE=/sys/src/ape
 <$APE/config
 LIB=/$objtype/lib/ape/libap.a
 OFILES=\
-	atom.$O\
 	cycles.$O\
 	getfcr.$O\
 	lock.$O\