NMI sampling

- if profile --nmi kernel uses NMI watchdog based sampling based on
  Intel architecture performance counters

- using NMI makes kernel profiling possible

- watchdog kernel lockup detection is disabled while sampling as we
  may get unpredictable interrupts in kernel and thus possibly many
  false positives

- if watchdog is not enabled at boot time, profiling enables it and
  turns it of again when done

kernel/watchdog.c

@@ -6,12 +6,13 @@
 
 #include "watchdog.h"
 #include "arch/i386/glo.h"
+#include "profile.h"
 
 unsigned watchdog_local_timer_ticks = 0U;
 struct arch_watchdog *watchdog;
 int watchdog_enabled;
 
-void nmi_watchdog_handler(struct nmi_frame * frame)
+PRIVATE void lockup_check(struct nmi_frame * frame)
 {
 	/* FIXME this should be CPU local */
 	static unsigned no_ticks;
@@ -23,7 +24,7 @@ void nmi_watchdog_handler(struct nmi_frame * frame)
 	 * report a lockup in such situation
 	 */
 	if (serial_debug_active)
-		goto reset_and_continue;
+		return;
 
 	if (last_tick_count != watchdog_local_timer_ticks) {
 		if (no_ticks == 1) {
@@ -32,7 +33,7 @@ void nmi_watchdog_handler(struct nmi_frame * frame)
 		}
 		/* we are still ticking, everything seems good */
 		last_tick_count = watchdog_local_timer_ticks;
-		goto reset_and_continue;
+		return;
 	}
 
 	/*
@@ -42,12 +43,63 @@ void nmi_watchdog_handler(struct nmi_frame * frame)
 	if (++no_ticks < 10) {
 		if (no_ticks == 1)
 			printf("WARNING watchdog : possible kernel lockup\n");
-		goto reset_and_continue;
+		return;
 	}
 
+	/* if we get this far, the kernel is locked up */
 	arch_watchdog_lockup(frame);
+}
 
-reset_and_continue:
-	if (watchdog->reinit)
+PUBLIC void nmi_watchdog_handler(struct nmi_frame * frame)
+{
+	/*
+	 * Do not check for lockups while profiling, it is extremely likely that
+	 * a false positive is detected if the frequency is high
+	 */
+	if (watchdog_enabled && !sprofiling)
+		lockup_check(frame);
+	if (sprofiling)
+		nmi_sprofile_handler(frame);
+	
+	if ((watchdog_enabled || sprofiling) && watchdog->reinit)
 		watchdog->reinit(cpuid);
 }
+
+int nmi_watchdog_start_profiling(const unsigned freq)
+{
+	int err;
+	
+	/* if watchdog hasn't been enabled, we must enable it now */
+	if (!watchdog_enabled) {
+		if (arch_watchdog_init())
+			return ENODEV;
+	}
+
+	if (!watchdog->profile_init) {
+		printf("WARNING NMI watchdog profiling not supported\n");
+		nmi_watchdog_stop_profiling();
+		return ENODEV;
+	}
+
+	err = watchdog->profile_init(freq);
+	if (err != OK)
+		return err;
+
+	watchdog->resetval = watchdog->profile_resetval;
+
+	return OK;
+}
+
+void nmi_watchdog_stop_profiling(void)
+{
+	/*
+	 * if we do not rearm the NMI source, we are done, if we want to keep
+	 * the watchdog running, we reset is to its normal value
+	 */
+
+	if (watchdog)
+		watchdog->resetval = watchdog->watchdog_resetval;
+
+	if (!watchdog_enabled)
+		arch_watchdog_stop();
+}