From: Martin Schwidefsky Sorting the list of clocksources according to their rating is not necessary as the clocksource selection is not performance critical. Simplify clocksource_register and sysfs_override_clocksource, remove clocksource_enqueue and let clocksource_select do the job. The check in clocksource_register for double registration of the same clocksource is removed without replacement. To find the initial clocksource a new weak function in jiffies.c is defined that returns the jiffies clocksource. The architecture code can then override the weak function with a more suitable clocksource, e.g. the TOD clock on s390. Cc: Ingo Molnar Cc: Thomas Gleixner Cc: john stultz Cc: Daniel Walker Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/time.c | 4 + include/linux/clocksource.h | 2 kernel/time/clocksource.c | 148 ++++++++++++++------------------------------ kernel/time/jiffies.c | 6 + kernel/time/timekeeping.c | 4 - 5 files changed, 62 insertions(+), 102 deletions(-) Index: linux-2.6/kernel/time/clocksource.c =================================================================== --- linux-2.6.orig/kernel/time/clocksource.c +++ linux-2.6/kernel/time/clocksource.c @@ -21,7 +21,6 @@ * * TODO WishList: * o Allow clocksource drivers to be unregistered - * o get rid of clocksource_jiffies extern */ #include @@ -107,9 +106,6 @@ u64 timecounter_cyc2time(struct timecoun } EXPORT_SYMBOL(timecounter_cyc2time); -/* XXX - Would like a better way for initializing curr_clocksource */ -extern struct clocksource clocksource_jiffies; - /*[Clocksource internal variables]--------- * curr_clocksource: * currently selected clocksource. Initialized to clocksource_jiffies. @@ -123,9 +119,8 @@ extern struct clocksource clocksource_ji * override_name: * Name of the user-specified clocksource. */ -static struct clocksource *curr_clocksource = &clocksource_jiffies; +static struct clocksource *curr_clocksource; static struct clocksource *next_clocksource; -static struct clocksource *clocksource_override; static LIST_HEAD(clocksource_list); static DEFINE_SPINLOCK(clocksource_lock); static char override_name[32]; @@ -320,6 +315,7 @@ void clocksource_touch_watchdog(void) clocksource_resume_watchdog(); } +#ifdef CONFIG_GENERIC_TIME /** * clocksource_get_next - Returns the selected clocksource * @@ -339,77 +335,69 @@ struct clocksource *clocksource_get_next } /** - * select_clocksource - Selects the best registered clocksource. - * - * Private function. Must hold clocksource_lock when called. - * - * Select the clocksource with the best rating, or the clocksource, - * which is selected by userspace override. + * clocksource_select - Select the best clocksource available */ -static struct clocksource *select_clocksource(void) +static int clocksource_select(void) { - struct clocksource *next; - - if (list_empty(&clocksource_list)) - return NULL; - - if (clocksource_override) - next = clocksource_override; - else - next = list_entry(clocksource_list.next, struct clocksource, - list); + struct clocksource *best, *cs; + int rc; - if (next == curr_clocksource) - return NULL; - - return next; -} - -/* - * Enqueue the clocksource sorted by rating - */ -static int clocksource_enqueue(struct clocksource *c) -{ - struct list_head *tmp, *entry = &clocksource_list; - - list_for_each(tmp, &clocksource_list) { - struct clocksource *cs; - - cs = list_entry(tmp, struct clocksource, list); - if (cs == c) - return -EBUSY; - /* Keep track of the place, where to insert */ - if (cs->rating >= c->rating) - entry = tmp; + rc = 0; + best = NULL; + list_for_each_entry(cs, &clocksource_list, list) { + /* Check for the override clocksource. */ + if (strcmp(cs->name, override_name) == 0) { + /* + * Check to make sure we don't switch to a non-highres + * capable clocksource if the tick code is in oneshot + * mode (highres or nohz) + */ + if ((cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) || + !tick_oneshot_mode_active()) { + /* Override clocksource can be used. */ + best = cs; + break; + } + /* Override clocksource cannot be used. */ + printk(KERN_WARNING "Override clocksource %s is not " + "HRT compatible. Cannot switch while in " + "HRT/NOHZ mode\n", cs->name); + override_name[0] = 0; + } + /* Check rating */ + if (!best || cs->rating > best->rating) + best = cs; } - list_add(&c->list, entry); + if (curr_clocksource != best) + next_clocksource = best; + return rc; +} - if (strlen(c->name) == strlen(override_name) && - !strcmp(c->name, override_name)) - clocksource_override = c; +#else /* CONFIG_GENERIC_TIME */ +static inline int clocksource_select(void) +{ return 0; } +#endif + /** * clocksource_register - Used to install new clocksources * @t: clocksource to be registered * * Returns -EBUSY if registration fails, zero otherwise. */ -int clocksource_register(struct clocksource *c) +int clocksource_register(struct clocksource *cs) { unsigned long flags; - int ret; spin_lock_irqsave(&clocksource_lock, flags); - ret = clocksource_enqueue(c); - if (!ret) - next_clocksource = select_clocksource(); + list_add(&cs->list, &clocksource_list); + clocksource_select(); spin_unlock_irqrestore(&clocksource_lock, flags); - if (!ret) - clocksource_check_watchdog(c); - return ret; + clocksource_check_watchdog(cs); + return 0; } EXPORT_SYMBOL(clocksource_register); @@ -422,10 +410,8 @@ void clocksource_change_rating(struct cl unsigned long flags; spin_lock_irqsave(&clocksource_lock, flags); - list_del(&cs->list); cs->rating = rating; - clocksource_enqueue(cs); - next_clocksource = select_clocksource(); + clocksource_select(); spin_unlock_irqrestore(&clocksource_lock, flags); } @@ -438,9 +424,7 @@ void clocksource_unregister(struct clock spin_lock_irqsave(&clocksource_lock, flags); list_del(&cs->list); - if (clocksource_override == cs) - clocksource_override = NULL; - next_clocksource = select_clocksource(); + clocksource_select(); spin_unlock_irqrestore(&clocksource_lock, flags); } @@ -478,10 +462,6 @@ static ssize_t sysfs_override_clocksourc struct sysdev_attribute *attr, const char *buf, size_t count) { - struct clocksource *ovr = NULL; - size_t ret = count; - int len; - /* strings from sysfs write are not 0 terminated! */ if (count >= sizeof(override_name)) return -EINVAL; @@ -495,41 +475,11 @@ static ssize_t sysfs_override_clocksourc if (count > 0) memcpy(override_name, buf, count); override_name[count] = 0; - - len = strlen(override_name); - if (len) { - struct clocksource *cs; - - ovr = clocksource_override; - /* try to select it: */ - list_for_each_entry(cs, &clocksource_list, list) { - if (strlen(cs->name) == len && - !strcmp(cs->name, override_name)) - ovr = cs; - } - } - - /* - * Check to make sure we don't switch to a non-highres capable - * clocksource if the tick code is in oneshot mode (highres or nohz) - */ - if (tick_oneshot_mode_active() && ovr && - !(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) { - printk(KERN_WARNING "%s clocksource is not HRT compatible. " - "Cannot switch while in HRT/NOHZ mode\n", ovr->name); - ovr = NULL; - override_name[0] = 0; - } - - /* Reselect, when the override name has changed */ - if (ovr != clocksource_override) { - clocksource_override = ovr; - next_clocksource = select_clocksource(); - } + clocksource_select(); spin_unlock_irq(&clocksource_lock); - return ret; + return count; } /** Index: linux-2.6/include/linux/clocksource.h =================================================================== --- linux-2.6.orig/include/linux/clocksource.h +++ linux-2.6/include/linux/clocksource.h @@ -14,6 +14,7 @@ #include #include #include +#include #include #include @@ -322,6 +323,7 @@ extern void clocksource_touch_watchdog(v extern struct clocksource* clocksource_get_next(void); extern void clocksource_change_rating(struct clocksource *cs, int rating); extern void clocksource_resume(void); +extern struct clocksource * __init __weak clocksource_default_clock(void); #ifdef CONFIG_GENERIC_TIME_VSYSCALL extern void update_vsyscall(struct timespec *ts, struct clocksource *c); Index: linux-2.6/kernel/time/timekeeping.c =================================================================== --- linux-2.6.orig/kernel/time/timekeeping.c +++ linux-2.6/kernel/time/timekeeping.c @@ -269,7 +269,7 @@ static void change_clocksource(void) new = clocksource_get_next(); - if (clock == new) + if (!new || clock == new) return; clocksource_forward_now(); @@ -436,7 +436,7 @@ void __init timekeeping_init(void) ntp_init(); - clock = clocksource_get_next(); + clock = clocksource_default_clock(); if (clock->enable) clock->enable(clock); /* save mult_orig on enable */ Index: linux-2.6/kernel/time/jiffies.c =================================================================== --- linux-2.6.orig/kernel/time/jiffies.c +++ linux-2.6/kernel/time/jiffies.c @@ -61,7 +61,6 @@ struct clocksource clocksource_jiffies = .read = jiffies_read, .mask = 0xffffffff, /*32bits*/ .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ - .mult_orig = NSEC_PER_JIFFY << JIFFIES_SHIFT, .shift = JIFFIES_SHIFT, }; @@ -71,3 +70,8 @@ static int __init init_jiffies_clocksour } core_initcall(init_jiffies_clocksource); + +struct clocksource * __init __weak clocksource_default_clock(void) +{ + return &clocksource_jiffies; +} Index: linux-2.6/arch/s390/kernel/time.c =================================================================== --- linux-2.6.orig/arch/s390/kernel/time.c +++ linux-2.6/arch/s390/kernel/time.c @@ -205,6 +205,10 @@ static struct clocksource clocksource_to .flags = CLOCK_SOURCE_IS_CONTINUOUS, }; +struct clocksource * __init clocksource_default_clock(void) +{ + return &clocksource_tod; +} void update_vsyscall(struct timespec *wall_time, struct clocksource *clock) { -- blue skies, Martin. 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