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.

4 files changed, 181 insertions, 5 deletions

diff --git a/sys/src/libc/mips/atom.s b/sys/src/libc/mips/atom.s
index b907f7f59..8975ac569 100644
--- a/sys/src/libc/mips/atom.s
+++ b/sys/src/libc/mips/atom.s
@@ -12,8 +12,7 @@ TEXT _xinc(SB), 1, $-4			/* void _xinc(long *); */
 loop:	MOVW	$1, R3
 	LL(2, 1)
 	NOOP
-	ADDU	R1, R3
-	MOVW	R3, R1			/* return new value */
+	ADD	R1,R3,R3
 	SC(2, 3)
 	NOOP
 	BEQ	R3,loop
@@ -25,8 +24,8 @@ TEXT _xdec(SB), 1, $-4			/* long _xdec(long *); */
 loop1:	MOVW	$-1, R3
 	LL(2, 1)
 	NOOP
-	ADDU	R1, R3
-	MOVW	R3, R1			/* return new value */
+	ADD	R1,R3,R3
+	MOVW	R3, R1
 	SC(2, 3)
 	NOOP
 	BEQ	R3,loop1
@@ -50,3 +49,9 @@ spincas:
 fail:
 	MOVW	$0, R1
 	RET
+
+/* general-purpose abort */
+_trap:
+	MOVD	$0, R0
+	MOVD	0(R0), R0
+	RET
diff --git a/sys/src/libc/mips/lock.c b/sys/src/libc/mips/lock.c
new file mode 100644
index 000000000..9c9bd2208
--- /dev/null
+++ b/sys/src/libc/mips/lock.c
@@ -0,0 +1,171 @@
+#include <u.h>
+#include <libc.h>
+
+enum
+{
+	Pagesize	= 4096,
+	Semperpg	= Pagesize/(16*sizeof(uint)),
+	Lockaddr	= 0x60000000,
+
+	POWER		= 0x320,
+	MAGNUM		= 0x330,
+	MAGNUMII	= 0x340,
+	R4K		= 0x500,
+};
+
+static	int arch;
+extern	int C_3ktas(int*);
+extern	int C_4ktas(int*);
+extern	int C_fcr0(void);
+
+static void
+lockinit(void)
+{
+	void *v;
+
+	if(arch != 0)
+		return;	/* allow multiple calls */
+	arch = C_fcr0();
+	switch(arch) {
+	case POWER:
+		v = (void*)Lockaddr;
+		if(segattach(SG_CEXEC, "lock", v, Pagesize) == (void*)-1) {
+			arch = MAGNUM;
+			break;
+		}
+		memset(v, 0, Pagesize);
+		break;
+	case MAGNUM:
+	case MAGNUMII:
+	case R4K:
+		break;
+	default:
+		arch = R4K;
+		break;
+	}
+}
+
+void
+lock(Lock *lk)
+{
+	int *hwsem;
+	int hash;
+
+retry:
+	switch(arch) {
+	case 0:
+		lockinit();
+		goto retry;
+	case MAGNUM:
+	case MAGNUMII:
+		while(C_3ktas(&lk->val))
+			sleep(0);
+		return;
+	case R4K:
+		for(;;){
+			while(lk->val)
+				;
+			if(C_4ktas(&lk->val) == 0)
+				return;
+		}
+		break;
+	case POWER:
+		/* Use low order lock bits to generate hash */
+		hash = ((int)lk/sizeof(int)) & (Semperpg-1);
+		hwsem = (int*)Lockaddr+hash;
+
+		for(;;) {
+			if((*hwsem & 1) == 0) {
+				if(lk->val)
+					*hwsem = 0;
+				else {
+					lk->val = 1;
+					*hwsem = 0;
+					return;
+				}
+			}
+			while(lk->val)
+				;
+		}
+	}
+}
+
+int
+canlock(Lock *lk)
+{
+	int *hwsem;
+	int hash;
+
+retry:
+	switch(arch) {
+	case 0:
+		lockinit();
+		goto retry;
+	case MAGNUM:
+	case MAGNUMII:
+		if(C_3ktas(&lk->val))
+			return 0;
+		return 1;
+	case R4K:
+		if(C_4ktas(&lk->val))
+			return 0;
+		return 1;
+	case POWER:
+		/* Use low order lock bits to generate hash */
+		hash = ((int)lk/sizeof(int)) & (Semperpg-1);
+		hwsem = (int*)Lockaddr+hash;
+
+		if((*hwsem & 1) == 0) {
+			if(lk->val)
+				*hwsem = 0;
+			else {
+				lk->val = 1;
+				*hwsem = 0;
+				return 1;
+			}
+		}
+		break;
+	}
+	return 0;
+}
+
+void
+unlock(Lock *lk)
+{
+	lk->val = 0;
+}
+
+int
+_tas(int *p)
+{
+	int *hwsem;
+	int hash;
+
+retry:
+	switch(arch) {
+	case 0:
+		lockinit();
+		goto retry;
+	case MAGNUM:
+	case MAGNUMII:
+		return C_3ktas(p);
+	case R4K:
+		return C_4ktas(p);
+	case POWER:
+		/* Use low order lock bits to generate hash */
+		hash = ((int)p/sizeof(int)) & (Semperpg-1);
+		hwsem = (int*)Lockaddr+hash;
+
+		if((*hwsem & 1) == 0) {
+			if(*p)
+				*hwsem = 0;
+			else {
+				*p = 1;
+				*hwsem = 0;
+				return 0;
+			}
+		}
+		break;
+	}
+	return 1;
+}
diff --git a/sys/src/libc/mips/mkfile b/sys/src/libc/mips/mkfile
index 460f7cd2f..3b902f6e3 100644
--- a/sys/src/libc/mips/mkfile
+++ b/sys/src/libc/mips/mkfile
@@ -23,6 +23,7 @@ SFILES=\
 
 CFILES=\
 	cycles.c\
+	lock.c\
 	notejmp.c\
 	sqrt.c\
 	vlrt.c\
diff --git a/sys/src/libc/mips/tas.s b/sys/src/libc/mips/tas.s
index a9bf40721..d754b21f6 100644
--- a/sys/src/libc/mips/tas.s
+++ b/sys/src/libc/mips/tas.s
@@ -17,7 +17,6 @@ btas:
 	BLTZ	R1, btas
 	RET
 
-	TEXT	_tas(SB),$0
 	TEXT	C_4ktas(SB), $0
 	MOVW	R1, R2		/* address of key */
 tas1: