shithub: riscv

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ref: 3794b1c14f15141eef839109871eb0d020023eff
parent: 4fc4b0dda73c8a04caff079ea358c53ed3dbfc71
author: cinap_lenrek <[email protected]>
date: Sat Oct 28 14:53:27 EDT 2017 

libc: improve alignment of QLp structure on amd64, cosmetics

the QLp structure used to occupy 24 bytes on amd64.
with some rearranging the fields we can get it to 16 bytes,
saving 8K in the data section for the 1024 preallocated
structs in the ql arena.

the rest of the changes are of cosmetic nature:

- getqlp() zeros the next pointer, so there is no need to set
  it when queueing the entry.

- always explicitely compare pointers to nil.

- delete unused code from ape's qlock.c


--- a/sys/include/ape/qlock.h
+++ b/sys/include/ape/qlock.h
@@ -13,8 +13,8 @@
 struct QLp
 {
 	int	inuse;
+	int	state;
 	QLp	*next;
-	char	state;
 };
 
 typedef
--- a/sys/include/libc.h
+++ b/sys/include/libc.h
@@ -435,8 +435,8 @@
 struct QLp
 {
 	int	inuse;
+	int	state;
 	QLp	*next;
-	char	state;
 };
 
 typedef
--- a/sys/src/ape/lib/ap/plan9/qlock.c
+++ b/sys/src/ape/lib/ap/plan9/qlock.c
@@ -22,9 +22,6 @@
 enum
 {
 	Queuing,
-	QueuingR,
-	QueuingW,
-	Sleeping,
 };
 
 /* find a free shared memory location to queue ourselves in */
@@ -41,10 +38,10 @@
 			abort();
 		if(_tas(&(p->inuse)) == 0){
 			ql.p = p;
-			p->next = nil;
 			break;
 		}
 	}
+	p->next = nil;
 	return p;
 }
 
@@ -60,7 +57,6 @@
 		return;
 	}
 
-
 	/* chain into waiting list */
 	mp = getqlp();
 	p = q->tail;
@@ -112,254 +108,3 @@
 	unlock(&q->lock);
 	return 0;
 }
-
-#if 0
-
-void
-rlock(RWLock *q)
-{
-	QLp *p, *mp;
-
-	lock(&q->lock);
-	if(q->writer == 0 && q->head == nil){
-		/* no writer, go for it */
-		q->readers++;
-		unlock(&q->lock);
-		return;
-	}
-
-	mp = getqlp();
-	p = q->tail;
-	if(p == 0)
-		q->head = mp;
-	else
-		p->next = mp;
-	q->tail = mp;
-	mp->next = nil;
-	mp->state = QueuingR;
-	unlock(&q->lock);
-
-	/* wait in kernel */
-	while((*_rendezvousp)(mp, (void*)1) == (void*)~0)
-		;
-	mp->inuse = 0;
-}
-
-int
-canrlock(RWLock *q)
-{
-	lock(&q->lock);
-	if (q->writer == 0 && q->head == nil) {
-		/* no writer; go for it */
-		q->readers++;
-		unlock(&q->lock);
-		return 1;
-	}
-	unlock(&q->lock);
-	return 0;
-}
-
-void
-runlock(RWLock *q)
-{
-	QLp *p;
-
-	lock(&q->lock);
-	if(q->readers <= 0)
-		abort();
-	p = q->head;
-	if(--(q->readers) > 0 || p == nil){
-		unlock(&q->lock);
-		return;
-	}
-
-	/* start waiting writer */
-	if(p->state != QueuingW)
-		abort();
-	q->head = p->next;
-	if(q->head == 0)
-		q->tail = 0;
-	q->writer = 1;
-	unlock(&q->lock);
-
-	/* wakeup waiter */
-	while((*_rendezvousp)(p, (void*)0) == (void*)~0)
-		;
-}
-
-void
-wlock(RWLock *q)
-{
-	QLp *p, *mp;
-
-	lock(&q->lock);
-	if(q->readers == 0 && q->writer == 0){
-		/* noone waiting, go for it */
-		q->writer = 1;
-		unlock(&q->lock);
-		return;
-	}
-
-	/* wait */
-	p = q->tail;
-	mp = getqlp();
-	if(p == nil)
-		q->head = mp;
-	else
-		p->next = mp;
-	q->tail = mp;
-	mp->next = nil;
-	mp->state = QueuingW;
-	unlock(&q->lock);
-
-	/* wait in kernel */
-	while((*_rendezvousp)(mp, (void*)1) == (void*)~0)
-		;
-	mp->inuse = 0;
-}
-
-int
-canwlock(RWLock *q)
-{
-	lock(&q->lock);
-	if (q->readers == 0 && q->writer == 0) {
-		/* no one waiting; go for it */
-		q->writer = 1;
-		unlock(&q->lock);
-		return 1;
-	}
-	unlock(&q->lock);
-	return 0;
-}
-
-void
-wunlock(RWLock *q)
-{
-	QLp *p;
-
-	lock(&q->lock);
-	if(q->writer == 0)
-		abort();
-	p = q->head;
-	if(p == nil){
-		q->writer = 0;
-		unlock(&q->lock);
-		return;
-	}
-	if(p->state == QueuingW){
-		/* start waiting writer */
-		q->head = p->next;
-		if(q->head == nil)
-			q->tail = nil;
-		unlock(&q->lock);
-		while((*_rendezvousp)(p, (void*)0) == (void*)~0)
-			;
-		return;
-	}
-
-	if(p->state != QueuingR)
-		abort();
-
-	/* wake waiting readers */
-	while(q->head != nil && q->head->state == QueuingR){
-		p = q->head;
-		q->head = p->next;
-		q->readers++;
-		while((*_rendezvousp)(p, (void*)0) == (void*)~0)
-			;
-	}
-	if(q->head == nil)
-		q->tail = nil;
-	q->writer = 0;
-	unlock(&q->lock);
-}
-
-void
-rsleep(Rendez *r)
-{
-	QLp *t, *me;
-
-	if(!r->l)
-		abort();
-	lock(&r->l->lock);
-	/* we should hold the qlock */
-	if(!r->l->locked)
-		abort();
-
-	/* add ourselves to the wait list */
-	me = getqlp();
-	me->state = Sleeping;
-	if(r->head == nil)
-		r->head = me;
-	else
-		r->tail->next = me;
-	me->next = nil;
-	r->tail = me;
-
-	/* pass the qlock to the next guy */
-	t = r->l->head;
-	if(t){
-		r->l->head = t->next;
-		if(r->l->head == nil)
-			r->l->tail = nil;
-		unlock(&r->l->lock);
-		while((*_rendezvousp)(t, (void*)0x12345) == (void*)~0)
-			;
-	}else{
-		r->l->locked = 0;
-		unlock(&r->l->lock);
-	}
-
-	/* wait for a wakeup */
-	while((*_rendezvousp)(me, (void*)1) == (void*)~0)
-		;
-	me->inuse = 0;
-}
-
-int
-rwakeup(Rendez *r)
-{
-	QLp *t;
-
-	/*
-	 * take off wait and put on front of queue
-	 * put on front so guys that have been waiting will not get starved
-	 */
-	
-	if(!r->l)
-		abort();
-	lock(&r->l->lock);
-	if(!r->l->locked)
-		abort();
-
-	t = r->head;
-	if(t == nil){
-		unlock(&r->l->lock);
-		return 0;
-	}
-
-	r->head = t->next;
-	if(r->head == nil)
-		r->tail = nil;
-
-	t->next = r->l->head;
-	r->l->head = t;
-	if(r->l->tail == nil)
-		r->l->tail = t;
-
-	t->state = Queuing;
-	unlock(&r->l->lock);
-	return 1;
-}
-
-int
-rwakeupall(Rendez *r)
-{
-	int i;
-
-	for(i=0; rwakeup(r); i++)
-		;
-	return i;
-}
-
-#endif
--- a/sys/src/libc/9sys/qlock.c
+++ b/sys/src/libc/9sys/qlock.c
@@ -39,10 +39,10 @@
 			abort();
 		if(_tas(&(p->inuse)) == 0){
 			ql.p = p;
-			p->next = nil;
 			break;
 		}
 	}
+	p->next = nil;
 	return p;
 }
 
@@ -128,12 +128,11 @@
 
 	mp = getqlp();
 	p = q->tail;
-	if(p == 0)
+	if(p == nil)
 		q->head = mp;
 	else
 		p->next = mp;
 	q->tail = mp;
-	mp->next = nil;
 	mp->state = QueuingR;
 	unlock(&q->lock);
 
@@ -199,14 +198,13 @@
 	}
 
 	/* wait */
-	p = q->tail;
 	mp = getqlp();
+	p = q->tail;
 	if(p == nil)
 		q->head = mp;
 	else
 		p->next = mp;
 	q->tail = mp;
-	mp->next = nil;
 	mp->state = QueuingW;
 	unlock(&q->lock);
 
@@ -286,7 +284,7 @@
 {
 	QLp *t, *me;
 
-	if(!r->l)
+	if(r->l == nil)
 		abort();
 	lock(&r->l->lock);
 	/* we should hold the qlock */
@@ -300,12 +298,11 @@
 		r->head = me;
 	else
 		r->tail->next = me;
-	me->next = nil;
 	r->tail = me;
 
 	/* pass the qlock to the next guy */
 	t = r->l->head;
-	if(t){
+	if(t != nil){
 		r->l->head = t->next;
 		if(r->l->head == nil)
 			r->l->tail = nil;
@@ -333,7 +330,7 @@
 	 * put on front so guys that have been waiting will not get starved
 	 */
 
-	if(!r->l)
+	if(r->l == nil)
 		abort();
 	lock(&r->l->lock);
 	if(!r->l->locked)