Module Name: src
Committed By: dyoung
Date: Fri Apr 30 21:05:27 UTC 2010
Modified Files:
src/sys/arch/x86/pci: pci_machdep.c
Log Message:
Add an exponential back-off to the loop that tries to lock the
PCI configuration-access registers, to avoid excessive cacheline
ping-ponging. Thanks to rmind@ for the tip.
To generate a diff of this commit:
cvs rdiff -u -r1.43 -r1.44 src/sys/arch/x86/pci/pci_machdep.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/x86/pci/pci_machdep.c
diff -u src/sys/arch/x86/pci/pci_machdep.c:1.43 src/sys/arch/x86/pci/pci_machdep.c:1.44
--- src/sys/arch/x86/pci/pci_machdep.c:1.43 Wed Apr 28 21:27:14 2010
+++ src/sys/arch/x86/pci/pci_machdep.c Fri Apr 30 21:05:27 2010
@@ -1,4 +1,4 @@
-/* $NetBSD: pci_machdep.c,v 1.43 2010/04/28 21:27:14 dyoung Exp $ */
+/* $NetBSD: pci_machdep.c,v 1.44 2010/04/30 21:05:27 dyoung Exp $ */
/*-
* Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
@@ -73,7 +73,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pci_machdep.c,v 1.43 2010/04/28 21:27:14 dyoung Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pci_machdep.c,v 1.44 2010/04/30 21:05:27 dyoung Exp $");
#include <sys/types.h>
#include <sys/param.h>
@@ -269,9 +269,21 @@
if (cpuno == cl->cl_cpuno) {
ocl->cl_cpuno = cpuno;
} else {
+ u_int spins;
+
ocl->cl_cpuno = 0;
- while (atomic_cas_32(&cl->cl_cpuno, 0, cpuno) != 0)
- ;
+
+ spins = SPINLOCK_BACKOFF_MIN;
+ while (atomic_cas_32(&cl->cl_cpuno, 0, cpuno) != 0) {
+ SPINLOCK_BACKOFF(spins);
+#ifdef LOCKDEBUG
+ if (SPINLOCK_SPINOUT(spins)) {
+ panic("%s: cpu %" PRId32
+ " spun out waiting for cpu %" PRId32,
+ __func__, cpuno, cl->cl_cpuno);
+ }
+#endif /* LOCKDEBUG */
+ }
}
/* Only one CPU can be here, so an interlocked atomic_swap(3)
