From 41171b9ebd84e6d78c77cd93ac7c18ddb444f22b Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Thu, 16 May 1996 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1996-05-16

---
 port/portdat.h |  1 +
 port/proc.c    | 25 ++++++++++++++++---------
 port/taslock.c | 20 +++++++++-----------
 3 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/port/portdat.h b/port/portdat.h
index 47dd3941ded2049f400d3db426da4f86c9dcc8c7..5d4251aa80999ee0c10e9ac48c33e9a31ee1405f 100644
--- a/port/portdat.h
+++ b/port/portdat.h
@@ -598,6 +598,7 @@ struct Proc
 	ulong	art;		/* avg # ticks used since last blocked */
 	ulong	movetime;	/* last time process switched processors */
 	ulong	readytime;	/* time process went ready */
+	ulong	lockpri;	/* priority of process holding lock we're trying for */
 
 	void	*ureg;		/* User registers for notes */
 	void	*dbgreg;	/* User registers for devproc */
diff --git a/port/proc.c b/port/proc.c
index 3686fbbcedc99199b263a17fd13bf31256d11c56..5d92c7dc12e7fc654e0cd943b581d65d7e4a9873 100644
--- a/port/proc.c
+++ b/port/proc.c
@@ -130,32 +130,39 @@ enum
 void
 ready(Proc *p)
 {
-	int s, pri;
+	int s, pri, base;
 	Schedq *rq;
 
 	s = splhi();
 
+	/*
+	 *  This interacts with code in taslock().  The intent is to keep the
+	 *  priority of a process trying for a lock lower than the process holding
+	 *  the lock.
+	 */
+	if(p->lockpri)
+		base = p->lockpri;
+	else
+		base = p->basepri;
+
 	/* history counts */
 	if(p->state == Running){
-		if(up->priority == PriLock){
-			pri = 0;
-		} else {
-			p->rt++;
-			pri = ((p->art + (p->rt<<1))>>2)/Squantum;
-		}
+		p->rt++;
+		pri = ((p->art + (p->rt<<1))>>2)/Squantum;
 	} else {
 		p->art = (p->art + (p->rt<<1))>>2;
 		p->rt = 0;
 		pri = p->art/Squantum;
 	}
-	pri = p->basepri - pri;
+	pri = base - pri;
 	if(pri < 0)
 		pri = 0;
 
 	/* the only intersection between the classes is at PriNormal */
-	if(pri < PriNormal && p->basepri > PriNormal)
+	if(pri < PriNormal && base > PriNormal)
 		pri = PriNormal;
 	p->priority = pri;
+
 	rq = &runq[p->priority];
 
 	lock(runq);
diff --git a/port/taslock.c b/port/taslock.c
index bf1e5f07e21fd7db6953af66446425c64da4571d..e01ef543af569207e2d8d156bea0583f7c7a93a9 100644
--- a/port/taslock.c
+++ b/port/taslock.c
@@ -25,18 +25,21 @@ lock(Lock *l)
 		for(i=0; i<1000000; i++)
 			if(tas(&l->key) == 0){
 				l->pc = pc;
+				l->pri = 0;
 				return;
 			}
 		lockloop(l, pc);
 		return;
 	}
 
+	/* priority interacts with code in ready() in proc.c */
 	pri = up->priority;
-	up->priority = PriLock;
 
 	for(i=0; i<1000; i++){
+		up->lockpri = l->pri;		/* assume priority of process holding lock */
 		if(tas(&l->key) == 0){
 			l->pri = pri;
+			up->lockpri = 0;	/* back to normal priority */
 			l->pc = pc;
 			return;
 		}
@@ -44,6 +47,7 @@ lock(Lock *l)
 			sched();
 	}
 	lockloop(l, pc);
+	up->lockpri = 0;	/* back to normal priority */
 }
 
 void
@@ -80,13 +84,11 @@ canlock(Lock *l)
 {
 	int pri;
 
-	SET(pri);
-	if(up) {
+	if(up)
 		pri = up->priority;
-		up->priority = PriLock;
-	}
+	else
+		pri = 0;
 	if(tas(&l->key)) {
-		up->priority = pri;
 		l->pc = getcallerpc(l);
 		return 0;
 	}
@@ -97,13 +99,9 @@ canlock(Lock *l)
 void
 unlock(Lock *l)
 {
-	int p;
-
-	p = l->pri;
 	l->pc = 0;
 	l->key = 0;
-	if(up != 0)
-		up->priority = p;
+	l->pri = 0;
 }
 
 void