From fc756652edad9b6ebcc7b58ed2e418b38d11f0b5 Mon Sep 17 00:00:00 2001
From: art <art@openbsd.org>
Date: Fri, 3 Mar 2000 16:49:24 +0000
Subject: [PATCH] Keep track of the number of times we trigger a reschedule
 before the context switch actually happens.

---
 sys/kern/kern_synch.c | 18 +++++++++++++++++-
 sys/sys/kernel.h      |  4 ++--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 4262d75af69..99b9abc9f20 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_synch.c,v 1.19 2000/03/03 11:46:09 art Exp $	*/
+/*	$OpenBSD: kern_synch.c,v 1.20 2000/03/03 16:49:25 art Exp $	*/
 /*	$NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $	*/
 
 /*-
@@ -64,6 +64,14 @@
 u_char	curpriority;		/* usrpri of curproc */
 int	lbolt;			/* once a second sleep address */
 
+/*
+ * We need to keep track on how many times we call roundrobin before we
+ * actually attempt a switch (that is when we call mi_switch()).
+ * This is done so that some slow kernel subsystems can yield instead of
+ * blocking the scheduling.
+ */
+int	roundrobin_attempts;
+
 void roundrobin __P((void *));
 void schedcpu __P((void *));
 void updatepri __P((struct proc *));
@@ -79,6 +87,7 @@ roundrobin(arg)
 {
 
 	need_resched();
+	roundrobin_attempts++;
 	timeout(roundrobin, NULL, hz / 10);
 }
 
@@ -630,6 +639,13 @@ mi_switch()
 #endif
 	cpu_switch(p);
 	microtime(&runtime);
+
+	/*
+	 * We reset roundrobin_attempts at exit, because cpu_switch could
+	 * have looped in the idle loop and the attempts would increase
+	 * leading to unjust punishment of an innocent process.
+	 */
+	roundrobin_attempts = 0;
 }
 
 /*
diff --git a/sys/sys/kernel.h b/sys/sys/kernel.h
index 6267f752a36..cfe2685c801 100644
--- a/sys/sys/kernel.h
+++ b/sys/sys/kernel.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kernel.h,v 1.5 1996/08/11 20:39:07 niklas Exp $	*/
+/*	$OpenBSD: kernel.h,v 1.6 2000/03/03 16:49:24 art Exp $	*/
 /*	$NetBSD: kernel.h,v 1.11 1995/03/03 01:24:16 cgd Exp $	*/
 
 /*-
@@ -67,5 +67,5 @@ extern int profhz;		/* profiling clock's frequency */
 extern int lbolt;		/* once a second sleep address */
 extern int tickdelta;
 extern long timedelta;
-
+extern int roundrobin_attempts;	/* number switch attempts before switch */
 
-- 
2.20.1