From e7d549fbd73cac17e80a5d85b48444f0142bc781 Mon Sep 17 00:00:00 2001
From: Ken Thompson <ken@golang.org>
Date: Wed, 16 Jul 2008 13:50:23 -0700
Subject: [PATCH] new (more fifo) schedulint algorithm newproc will reuse dead
 procs

SVN=127565
---
 src/runtime/proc.c    | 47 +++++++++++++++++++++++++++++++------------
 src/runtime/runtime.h |  5 +++--
 2 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/src/runtime/proc.c b/src/runtime/proc.c
index fee6255a1b..d6aed85f1c 100644
--- a/src/runtime/proc.c
+++ b/src/runtime/proc.c
@@ -35,8 +35,24 @@ sys·newproc(int32 siz, byte* fn, byte* arg0)
 		sys·panicl(123);
 	}
 
-	newg = mal(sizeof(G));
-	stk = mal(4096);
+	// try to rip off an old goroutine
+	for(newg=allg; newg!=nil; newg=newg->alllink)
+		if(newg->status == Gdead)
+			break;
+
+	if(newg == nil) {
+		newg = mal(sizeof(G));
+		stk = mal(4096);
+		newg->stack0 = stk;
+
+		newg->status = Gwaiting;
+		newg->alllink = allg;
+		allg = newg;
+	} else {
+		stk = newg->stack0;
+		newg->status = Gwaiting;
+	}
+
 	newg->stackguard = stk+160;
 
 	sp = stk + 4096 - 4*8;
@@ -56,8 +72,6 @@ sys·newproc(int32 siz, byte* fn, byte* arg0)
 	newg->goid = goidgen;
 
 	newg->status = Grunnable;
-	newg->alllink = allg;
-	allg = newg;
 
 //prints(" goid=");
 //sys·printint(newg->goid);
@@ -67,18 +81,25 @@ sys·newproc(int32 siz, byte* fn, byte* arg0)
 G*
 select(void)
 {
-	G *gp, *bestg;
+	G *gp;
 
-	bestg = nil;
+	gp = m->lastg;
+	if(gp == nil)
+		gp = allg;
+
+	for(gp=gp->alllink; gp!=nil; gp=gp->alllink) {
+		if(gp->status == Grunnable) {
+			m->lastg = gp;
+			return gp;
+		}
+	}
 	for(gp=allg; gp!=nil; gp=gp->alllink) {
-		if(gp->status != Grunnable)
-			continue;
-		if(bestg == nil || gp->pri < bestg->pri)
-			bestg = gp;
+		if(gp->status == Grunnable) {
+			m->lastg = gp;
+			return gp;
+		}
 	}
-	if(bestg != nil)
-		bestg->pri++;
-	return bestg;
+	return nil;
 }
 
 void
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index dec63eaa76..b1e8b69b25 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -105,11 +105,11 @@ struct	G
 {
 	byte*	stackguard;	// must not move
 	byte*	stackbase;	// must not move
+	byte*	stack0;		// first stack segment
 	Gobuf	sched;
 	G*	alllink;	// on allq
 	G*	qlink;		// on wait q
 	int32	status;
-	int32	pri;
 	int32	goid;
 	byte	elem[8];	// transfer element for chan
 };
@@ -117,8 +117,9 @@ struct	M
 {
 	G*	g0;		// g0 w interrupt stack - must not move
 	uint64	morearg;	// arg to morestack - must not move
-	uint64	cret;	// return value from C - must not move
+	uint64	cret;		// return value from C - must not move
 	G*	curg;		// current running goroutine
+	G*	lastg;		// last running goroutine - to emulate fifo
 	Gobuf	sched;
 	Gobuf	morestack;
 	byte*	moresp;
-- 
2.48.1