From 06615ccb3a78cefb138d77a2fbc7e1700dbe8b23 Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@dragonflybsd.org>
Date: Mon, 2 Jul 2007 16:52:01 +0000
Subject: [PATCH] Implement an architecture call for contended spinlocks so the
 vkernel can insert a usleep().

---
 sys/kern/kern_spinlock.c             |  3 ++-
 sys/platform/pc32/i386/machdep.c     | 13 ++++++++++++-
 sys/platform/vkernel/i386/cpu_regs.c | 12 +++++++++++-
 sys/sys/systm.h                      |  3 ++-
 4 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/sys/kern/kern_spinlock.c b/sys/kern/kern_spinlock.c
index f83acccb3a..a96645e7a8 100644
--- a/sys/kern/kern_spinlock.c
+++ b/sys/kern/kern_spinlock.c
@@ -29,7 +29,7 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- * $DragonFly: src/sys/kern/kern_spinlock.c,v 1.10 2007/02/21 02:19:39 corecode Exp $
+ * $DragonFly: src/sys/kern/kern_spinlock.c,v 1.11 2007/07/02 16:51:58 dillon Exp $
  */
 
 #include <sys/param.h>
@@ -262,6 +262,7 @@ exponential_backoff(struct exponential_backoff *bo)
 	 * Indefinite
 	 */
 	++spinlocks_contested2;
+	cpu_spinlock_contested();
 	if (bo->nsec == 0) {
 		bo->base = sys_cputimer->count();
 		bo->nsec = 1;
diff --git a/sys/platform/pc32/i386/machdep.c b/sys/platform/pc32/i386/machdep.c
index f650aa77ab..7964cfe36b 100644
--- a/sys/platform/pc32/i386/machdep.c
+++ b/sys/platform/pc32/i386/machdep.c
@@ -36,7 +36,7 @@
  *
  *	from: @(#)machdep.c	7.4 (Berkeley) 6/3/91
  * $FreeBSD: src/sys/i386/i386/machdep.c,v 1.385.2.30 2003/05/31 08:48:05 alc Exp $
- * $DragonFly: src/sys/platform/pc32/i386/machdep.c,v 1.126 2007/07/02 01:37:09 dillon Exp $
+ * $DragonFly: src/sys/platform/pc32/i386/machdep.c,v 1.127 2007/07/02 16:52:01 dillon Exp $
  */
 
 #include "use_apm.h"
@@ -959,6 +959,17 @@ cpu_mplock_contested(void)
 	cpu_pause();
 }
 
+/*
+ * This routine is called if a spinlock has been held through the
+ * exponential backoff period and is seriously contested.  On a real cpu
+ * we let it spin.
+ */
+void
+cpu_spinlock_contested(void)
+{
+	cpu_pause();
+}
+
 /*
  * Clear registers on exec
  */
diff --git a/sys/platform/vkernel/i386/cpu_regs.c b/sys/platform/vkernel/i386/cpu_regs.c
index 9fbcb833bf..e502a3c254 100644
--- a/sys/platform/vkernel/i386/cpu_regs.c
+++ b/sys/platform/vkernel/i386/cpu_regs.c
@@ -37,7 +37,7 @@
  *
  *	from: @(#)machdep.c	7.4 (Berkeley) 6/3/91
  * $FreeBSD: src/sys/i386/i386/machdep.c,v 1.385.2.30 2003/05/31 08:48:05 alc Exp $
- * $DragonFly: src/sys/platform/vkernel/i386/cpu_regs.c,v 1.20 2007/07/02 06:30:26 dillon Exp $
+ * $DragonFly: src/sys/platform/vkernel/i386/cpu_regs.c,v 1.21 2007/07/02 16:52:00 dillon Exp $
  */
 
 #include "use_ether.h"
@@ -749,6 +749,16 @@ cpu_mplock_contested(void)
 	usleep(1000);
 }
 
+/*
+ * Called by the spinlock code with or without a critical section held
+ * when a spinlock is found to be seriously constested.
+ */
+void
+cpu_spinlock_contested(void)
+{
+	usleep(1000);
+}
+
 #endif
 
 /*
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index 6ac300bdac..688cc111ff 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -37,7 +37,7 @@
  *
  *	@(#)systm.h	8.7 (Berkeley) 3/29/95
  * $FreeBSD: src/sys/sys/systm.h,v 1.111.2.18 2002/12/17 18:04:02 sam Exp $
- * $DragonFly: src/sys/sys/systm.h,v 1.72 2007/07/02 01:37:11 dillon Exp $
+ * $DragonFly: src/sys/sys/systm.h,v 1.73 2007/07/02 16:52:01 dillon Exp $
  */
 
 #ifndef _SYS_SYSTM_H_
@@ -147,6 +147,7 @@ void	*phashinit (int count, struct malloc_type *type, u_long *nentries);
 int	cpu_sanitize_frame (struct trapframe *);
 int	cpu_sanitize_tls (struct savetls *);
 void	cpu_mplock_contested(void);
+void	cpu_spinlock_contested(void);
 void	cpu_halt (void);
 void	cpu_reset (void);
 void	cpu_boot (int);
-- 
2.41.0