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, 14 insertions, 82 deletions

diff --git a/sys/src/ape/lib/ap/arm/atom.s b/sys/src/ape/lib/ap/arm/atom.s
deleted file mode 100644
index b59a89d90..000000000
--- a/sys/src/ape/lib/ap/arm/atom.s
+++ /dev/null
@@ -1,58 +0,0 @@
-#define	CLREX		WORD	$0xf57ff01f
-#define	LDREX(a,r)	WORD	$(0xe<<28|0x01900f9f | (a)<<16 | (r)<<12)
-/* `The order of operands is from left to right in dataflow order' - asm man */
-#define	STREX(v,a,r)	WORD	$(0xe<<28|0x01800f90 | (a)<<16 | (r)<<12 | (v)<<0)
-
-/*
- * int cas(ulong *p, ulong ov, ulong nv);
- */
-
-TEXT	cas+0(SB),0,$0		/* r0 holds p */
-TEXT	casp+0(SB),0,$0		/* r0 holds p */
-	MOVW	ov+4(FP), R1
-	MOVW	nv+8(FP), R2
-spincas:
-	LDREX(0,3)	/*	LDREX	0(R0),R3	*/
-	CMP.S	R3, R1
-	BNE	fail
-	STREX(2,0,4)	/*	STREX	0(R0),R2,R4	*/
-	CMP.S	$0, R4
-	BNE	spincas
-	MOVW	$1, R0
-	RET
-fail:
-	CLREX
-	MOVW	$0, R0
-	RET
-
-TEXT _xinc(SB), $0	/* void	_xinc(long *); */
-TEXT ainc(SB), $0	/* long ainc(long *); */
-spinainc:
-	LDREX(0,3)	/*	LDREX	0(R0),R3	*/
-	ADD	$1,R3
-	STREX(3,0,4)	/*	STREX	0(R0),R3,R4	*/
-	CMP.S	$0, R4
-	BNE	spinainc
-	MOVW	R3, R0
-	RET
-
-TEXT _xdec(SB), $0	/* long _xdec(long *); */
-TEXT adec(SB), $0	/* long adec(long *); */
-spinadec:
-	LDREX(0,3)	/*	LDREX	0(R0),R3	*/
-	SUB	$1,R3
-	STREX(3,0,4)	/*	STREX	0(R0),R3,R4	*/
-	CMP.S	$0, R4
-	BNE	spinadec
-	MOVW	R3, R0
-	RET
-
-TEXT loadlinked(SB), $0	/* long loadlinked(long *); */
-	LDREX(0,0)	/*	LDREX	0(R0),R0	*/
-	RET
-
-TEXT storecond(SB), $0	/* int storecond(long *, long); */
-	MOVW	ov+4(FP), R3
-	STREX(3,0,0)	/*	STREX	0(R0),R3,R0	*/
-	RSB	$1, R0
-	RET
diff --git a/sys/src/ape/lib/ap/arm/lock.c b/sys/src/ape/lib/ap/arm/lock.c
index 65a65df7b..91c0ba233 100644
--- a/sys/src/ape/lib/ap/arm/lock.c
+++ b/sys/src/ape/lib/ap/arm/lock.c
@@ -1,35 +1,26 @@
-#include "../plan9/lib.h"
-#include "../plan9/sys9.h"
 #define _LOCK_EXTENSION
+#include "../plan9/sys9.h"
 #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 */
-	}
+	while(tas(&lk->val))
+		_SLEEP(0);
 }
 
-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/arm/mkfile b/sys/src/ape/lib/ap/arm/mkfile
index 97d0fa80b..f65e34395 100644
--- a/sys/src/ape/lib/ap/arm/mkfile
+++ b/sys/src/ape/lib/ap/arm/mkfile
@@ -2,7 +2,6 @@ APE=/sys/src/ape
 <$APE/config
 LIB=/$objtype/lib/ape/libap.a
 OFILES=\
-	atom.$O\
 	cycles.$O\
 	div.$O\
 	getfcr.$O\