Modifies the way clocks are switched to in the timekeeping code. The original code would constantly monitor the clocksource list checking for newly added clocksources. I modified this by using atomic types to signal when a new clock is added. This allows the operation to be used only when it's needed. The fast path is also reduced to checking a single atomic value. Signed-Off-By: Daniel Walker --- include/linux/clocksource.h | 5 ++++ include/linux/timekeeping.h | 10 -------- kernel/time/clocksource.c | 6 +++++ kernel/time/timekeeping.c | 51 +++++++++++++++++++++++++++++++------------- 4 files changed, 49 insertions(+), 23 deletions(-) Index: linux-2.6.19/include/linux/clocksource.h =================================================================== --- linux-2.6.19.orig/include/linux/clocksource.h +++ linux-2.6.19/include/linux/clocksource.h @@ -26,6 +26,11 @@ typedef u64 cycle_t; extern struct clocksource clocksource_jiffies; /* + * Atomic signal that is specific to timekeeping. + */ +extern atomic_t clock_check; + +/* * Allows inlined calling for notifier routines. */ extern struct atomic_notifier_head clocksource_list_notifier; Index: linux-2.6.19/include/linux/timekeeping.h =================================================================== --- linux-2.6.19.orig/include/linux/timekeeping.h +++ linux-2.6.19/include/linux/timekeeping.h @@ -5,15 +5,7 @@ extern void update_wall_time(void); -#ifdef CONFIG_GENERIC_TIME - -extern struct clocksource *clock; - -#else /* CONFIG_GENERIC_TIME */ -static inline int change_clocksource(void) -{ - return 0; -} +#ifndef CONFIG_GENERIC_TIME static inline void change_clocksource(void) { } static inline void timekeeping_init_notifier(void) { } Index: linux-2.6.19/kernel/time/clocksource.c =================================================================== --- linux-2.6.19.orig/kernel/time/clocksource.c +++ linux-2.6.19/kernel/time/clocksource.c @@ -50,6 +50,7 @@ static char override_name[32]; static int finished_booting; ATOMIC_NOTIFIER_HEAD(clocksource_list_notifier); +atomic_t clock_check = ATOMIC_INIT(0); /* clocksource_done_booting - Called near the end of bootup * @@ -58,6 +59,8 @@ ATOMIC_NOTIFIER_HEAD(clocksource_list_no static int __init clocksource_done_booting(void) { finished_booting = 1; + /* Check for a new clock now */ + atomic_inc(&clock_check); return 0; } @@ -291,6 +294,9 @@ static ssize_t sysfs_override_clocksourc /* try to select it: */ next_clocksource = select_clocksource(); + /* Signal that there is a new clocksource */ + atomic_inc(&clock_check); + spin_unlock_irq(&clocksource_lock); return ret; Index: linux-2.6.19/kernel/time/timekeeping.c =================================================================== --- linux-2.6.19.orig/kernel/time/timekeeping.c +++ linux-2.6.19/kernel/time/timekeeping.c @@ -3,6 +3,7 @@ #include #include #include +#include #include /* @@ -19,7 +20,6 @@ static unsigned long timekeeping_suspend * Clock used for timekeeping */ struct clocksource *clock = &clocksource_jiffies; -atomic_t clock_recalc_interval = ATOMIC_INIT(0); /* * The current time @@ -150,11 +150,12 @@ int do_settimeofday(struct timespec *tv) EXPORT_SYMBOL(do_settimeofday); /** - * change_clocksource - Swaps clocksources if a new one is available + * timkeeping_change_clocksource - Swaps clocksources if a new one is available * * Accumulates current time interval and initializes new clocksource + * Needs to be called with the xtime_lock held. */ -static int change_clocksource(void) +static int timekeeping_change_clocksource(void) { struct clocksource *new; cycle_t now; @@ -169,9 +170,15 @@ static int change_clocksource(void) clock->cycle_last = now; printk(KERN_INFO "Time: %s clocksource has been installed.\n", clock->name); + hrtimer_clock_notify(); + clock->error = 0; + clock->xtime_nsec = 0; + clocksource_calculate_interval(clock, tick_nsec); return 1; - } else if (unlikely(atomic_read(&clock_recalc_interval))) { - atomic_set(&clock_recalc_interval, 0); + } else { + clock->error = 0; + clock->xtime_nsec = 0; + clocksource_calculate_interval(clock, tick_nsec); return 1; } return 0; @@ -198,9 +205,14 @@ int timekeeping_is_continuous(void) static int clocksource_callback(struct notifier_block *nb, unsigned long op, void *c) { - if (c == clock && op == CLOCKSOURCE_NOTIFY_FREQ && - !atomic_read(&clock_recalc_interval)) - atomic_inc(&clock_recalc_interval); + if (likely(c != clock)) + return 0; + + switch (op) { + case CLOCKSOURCE_NOTIFY_FREQ: + case CLOCKSOURCE_NOTIFY_RATING: + atomic_inc(&clock_check); + } return 0; } @@ -325,6 +337,13 @@ static int __init timekeeping_init_devic int error = sysdev_class_register(&timekeeping_sysclass); if (!error) error = sysdev_register(&device_timer); + +#ifdef CONFIG_GENERIC_TIME + /* + * Now we signal to switch to a high-res clock. + */ + atomic_inc(&clock_check); +#endif return error; } @@ -467,13 +486,17 @@ 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 */ - if (change_clocksource()) { - clock->error = 0; - clock->xtime_nsec = 0; - hrtimer_clock_notify(); - clocksource_calculate_interval(clock, tick_nsec); +#ifdef CONFIG_GENERIC_TIME + /* + * check to see if there is a new clocksource to use + */ + if (unlikely(atomic_read(&clock_check))) { + + timekeeping_change_clocksource(); + + atomic_set(&clock_check, 0); } +#endif /* CONFIG_GENERIC_TIME */ update_vsyscall(&xtime, clock); } -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/