Index: linux-2.6.8-rc1/arch/i386/Kconfig
===================================================================
--- linux-2.6.8-rc1.orig/arch/i386/Kconfig	2004-07-12 16:11:43.531241636 +1000
+++ linux-2.6.8-rc1/arch/i386/Kconfig	2004-07-12 16:12:45.036678502 +1000
@@ -504,6 +504,13 @@
 	  Say Y here if you are building a kernel for a desktop, embedded
 	  or real-time system.  Say N if you are unsure.
 
+config PREEMPT_TIMING
+	bool "Non-preemptible critical section timing"
+	help
+	  This option measures the time spent in non-preemptible critical
+	  sections and reports warnings when a boot-time configurable
+	  latency threshold is exceeded.
+
 config X86_UP_APIC
 	bool "Local APIC support on uniprocessors" if !SMP
 	depends on !(X86_VISWS || X86_VOYAGER)
Index: linux-2.6.8-rc1/arch/i386/kernel/traps.c
===================================================================
--- linux-2.6.8-rc1.orig/arch/i386/kernel/traps.c	2004-07-12 16:11:43.601230753 +1000
+++ linux-2.6.8-rc1/arch/i386/kernel/traps.c	2004-07-12 16:12:45.037678346 +1000
@@ -947,3 +947,68 @@
 
 	trap_init_hook();
 }
+
+#ifdef CONFIG_PREEMPT_TIMING
+
+static int preempt_thresh;
+static DEFINE_PER_CPU(u64, preempt_timings);
+static DEFINE_PER_CPU(unsigned long, preempt_entry);
+static DEFINE_PER_CPU(unsigned long, preempt_exit);
+
+static int setup_preempt_thresh(char *s)
+{
+	int thresh;
+
+	get_option(&s, &thresh);
+	if (thresh > 0) {
+		preempt_thresh = thresh;
+		printk("Preemption threshold = %dms\n", preempt_thresh);
+	}
+	return 1;
+}
+__setup("preempt_thresh=", setup_preempt_thresh);
+
+void __inc_preempt_count(void)
+{
+	preempt_count()++;
+	if (preempt_count() == 1 && system_state == SYSTEM_RUNNING) {
+		rdtscll(__get_cpu_var(preempt_timings));
+		__get_cpu_var(preempt_entry)
+				= (unsigned long)__builtin_return_address(0);
+	}
+}
+
+void __dec_preempt_count(void)
+{
+	if (preempt_count() == 1 && system_state == SYSTEM_RUNNING &&
+					__get_cpu_var(preempt_entry)) {
+		u64 exit;
+		__get_cpu_var(preempt_exit)
+				= (unsigned long)__builtin_return_address(0);
+		rdtscll(exit);
+		if (cpu_khz) {
+			__get_cpu_var(preempt_timings) =
+				exit - __get_cpu_var(preempt_timings);
+			do_div(__get_cpu_var(preempt_timings), cpu_khz);
+			if (__get_cpu_var(preempt_timings) > preempt_thresh &&
+							preempt_thresh) {
+				printk("%lums non-preemptible critical "
+					"section violated %d ms preempt "
+					"threshold starting at ",
+					(unsigned long)
+						__get_cpu_var(preempt_timings),
+					preempt_thresh);
+				print_symbol("%s and ending at ",
+					__get_cpu_var(preempt_entry));
+				print_symbol("%s\n",
+					__get_cpu_var(preempt_exit));
+				dump_stack();
+			}
+		}
+		__get_cpu_var(preempt_exit) = __get_cpu_var(preempt_entry) = 0;
+	}
+	preempt_count()--;
+}
+EXPORT_SYMBOL(__inc_preempt_count);
+EXPORT_SYMBOL(__dec_preempt_count);
+#endif
Index: linux-2.6.8-rc1/include/linux/preempt.h
===================================================================
--- linux-2.6.8-rc1.orig/include/linux/preempt.h	2004-03-11 21:29:26.000000000 +1100
+++ linux-2.6.8-rc1/include/linux/preempt.h	2004-07-12 16:12:45.055675548 +1000
@@ -9,17 +9,22 @@
 #include <linux/config.h>
 #include <linux/linkage.h>
 
-#define preempt_count()	(current_thread_info()->preempt_count)
-
-#define inc_preempt_count() \
-do { \
-	preempt_count()++; \
-} while (0)
+#ifdef CONFIG_PREEMPT_TIMING
+void __inc_preempt_count(void);
+void __dec_preempt_count(void);
+#else
+#ifdef CONFIG_PREEMPT
+#define __inc_preempt_count()	do { preempt_count()++; } while (0)
+#define __dec_preempt_count()	do { preempt_count()--; } while (0)
+#else
+#define __inc_preempt_count()	do { } while (0)
+#define __dec_preempt_count()	do { } while (0)
+#endif
+#endif
 
-#define dec_preempt_count() \
-do { \
-	preempt_count()--; \
-} while (0)
+#define preempt_count()	(current_thread_info()->preempt_count)
+#define inc_preempt_count()	__inc_preempt_count()
+#define dec_preempt_count()	__dec_preempt_count()
 
 #ifdef CONFIG_PREEMPT
 
@@ -51,9 +56,9 @@
 
 #else
 
-#define preempt_disable()		do { } while (0)
-#define preempt_enable_no_resched()	do { } while (0)
-#define preempt_enable()		do { } while (0)
+#define preempt_disable()		__inc_preempt_count()
+#define preempt_enable_no_resched()	__dec_preempt_count()
+#define preempt_enable()		__dec_preempt_count()
 #define preempt_check_resched()		do { } while (0)
 
 #endif