[PATCH] timekeeping: drop irq-context clocksource polling

[Daniel Walker <dwalker@mvista.com>]

Before this change the timekeeping code would poll the clocksource
list every interrupt. This changes that so the clocksource list is
only checked when there has been and update, and no longer checks
in interrupt context.

This also has a few small space and line cleanups.

Boot tested on i386, compile tested on x86_64 .. However, I couldn't
find a !GENERIC_TIME that compiled without this change so it's untested..

Signed-Off-By: Daniel Walker <dwalker@mvista.com>

---
 include/linux/timekeeping.h |   10 ++++++++++
 kernel/time/clocksource.c   |    7 +++++++
 kernel/time/timekeeping.c   |   17 ++++++++---------
 3 files changed, 25 insertions(+), 9 deletions(-)

Index: linux-2.6.20/include/linux/timekeeping.h
===================================================================
--- /dev/null
+++ linux-2.6.20/include/linux/timekeeping.h
@@ -0,0 +1,10 @@
+#ifndef _LINUX_TIMEKEEPING_H
+#define _LINUX_TIMEKEEPING_H
+
+#ifdef CONFIG_GENERIC_TIME
+extern void timekeeping_change_clocksource(void);
+#else
+static inline void timekeeping_change_clocksource(void) { }
+#endif
+
+#endif
Index: linux-2.6.20/kernel/time/clocksource.c
===================================================================
--- linux-2.6.20.orig/kernel/time/clocksource.c
+++ linux-2.6.20/kernel/time/clocksource.c
@@ -30,6 +30,7 @@
 #include <linux/module.h>
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
 #include <linux/tick.h>
+#include <linux/timekeeping.h>
 
 /* XXX - Would like a better way for initializing curr_clocksource */
 extern struct clocksource clocksource_jiffies;
@@ -279,6 +280,8 @@ int clocksource_register(struct clocksou
 
 	clocksource_check_watchdog(c);
 
+	timekeeping_change_clocksource();
+
 	return 0;
 }
 EXPORT_SYMBOL(clocksource_register);
@@ -297,6 +300,8 @@ void clocksource_change_rating(struct cl
 	clocksource_enqueue(cs);
 	next_clocksource = select_clocksource();
 	spin_unlock_irqrestore(&clocksource_lock, flags);
+
+	timekeeping_change_clocksource();
 }
 
 #ifdef CONFIG_SYSFS
@@ -374,6 +379,8 @@ static ssize_t sysfs_override_clocksourc
 
 	spin_unlock_irq(&clocksource_lock);
 
+	timekeeping_change_clocksource();
+
 	return ret;
 }
 
Index: linux-2.6.20/kernel/time/timekeeping.c
===================================================================
--- linux-2.6.20.orig/kernel/time/timekeeping.c
+++ linux-2.6.20/kernel/time/timekeeping.c
@@ -18,7 +18,7 @@
 #include <linux/jiffies.h>
 #include <linux/time.h>
 #include <linux/tick.h>
-
+#include <linux/timekeeping.h>
 
 /*
  * This read-write spinlock protects us from races in SMP while
@@ -42,10 +42,8 @@ struct timespec wall_to_monotonic __attr
 
 EXPORT_SYMBOL(xtime);
 
-
 static struct clocksource *clock; /* pointer to current clocksource */
 
-
 #ifdef CONFIG_GENERIC_TIME
 /**
  * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
@@ -168,9 +166,10 @@ EXPORT_SYMBOL(do_settimeofday);
  *
  * Accumulates current time interval and initializes new clocksource
  */
-static void change_clocksource(void)
+void timekeeping_change_clocksource(void)
 {
 	struct clocksource *new;
+	unsigned long flags;
 	cycle_t now;
 	u64 nsec;
 
@@ -179,8 +178,10 @@ static void change_clocksource(void)
 	if (clock == new)
 		return;
 
+	write_seqlock_irqsave(&xtime_lock, flags);
+
 	now = clocksource_read(new);
-	nsec =  __get_nsec_offset();
+	nsec = __get_nsec_offset();
 	timespec_add_ns(&xtime, nsec);
 
 	clock = new;
@@ -192,11 +193,11 @@ static void change_clocksource(void)
 
 	tick_clock_notify();
 
+	write_sequnlock_irqrestore(&xtime_lock, flags);
+
 	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
 	       clock->name);
 }
-#else
-static inline void change_clocksource(void) { }
 #endif
 
 /**
@@ -470,7 +471,5 @@ void update_wall_time(void)
 	xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
 	clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
 
-	/* check to see if there is a new clocksource to use */
-	change_clocksource();
 	update_vsyscall(&xtime, clock);
 }
-- 

--