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SubjectRe: [RFC][patch 2/5] cleanup clocksource selection
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On Tue, 2009-07-21 at 21:17 +0200, Martin Schwidefsky wrote:
> plain text document attachment (clocksource-queue.diff)
> From: Martin Schwidefsky <schwidefsky@de.ibm.com>
>
> Introduce clocksource_dequeue & clocksource_update and move spinlock
> calls. clocksource_update does nothing for GENERIC_TIME=n since
> change_clocksource does nothing as well.
>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: john stultz <johnstul@us.ibm.com>
> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
> ---
> kernel/time/clocksource.c | 123 ++++++++++++++++++++++++++--------------------
> 1 file changed, 70 insertions(+), 53 deletions(-)


>From a very quick skim, this patch looks structurally ok to me.

thanks
-john


> Index: linux-2.6/kernel/time/clocksource.c
> ===================================================================
> --- linux-2.6.orig/kernel/time/clocksource.c
> +++ linux-2.6/kernel/time/clocksource.c
> @@ -341,46 +341,25 @@ struct clocksource *clocksource_get_next
> return curr_clocksource;
> }
>
> -/**
> - * 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.
> - */
> -static struct clocksource *select_clocksource(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);
> -
> - 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;
> + unsigned long flags;
> + int rc;
>
> + spin_lock_irqsave(&clocksource_lock, flags);
> + rc = 0;
> list_for_each(tmp, &clocksource_list) {
> struct clocksource *cs;
>
> cs = list_entry(tmp, struct clocksource, list);
> - if (cs == c)
> - return -EBUSY;
> + if (cs == c) {
> + rc = -EBUSY;
> + goto out;
> + }
> /* Keep track of the place, where to insert */
> if (cs->rating >= c->rating)
> entry = tmp;
> @@ -390,8 +369,23 @@ static int clocksource_enqueue(struct cl
> if (strlen(c->name) == strlen(override_name) &&
> !strcmp(c->name, override_name))
> clocksource_override = c;
> +out:
> + spin_unlock_irqrestore(&clocksource_lock, flags);
> + return rc;
> +}
> +
> +/*
> + * Dequeue a clocksource
> + */
> +static void clocksource_dequeue(struct clocksource *cs)
> +{
> + unsigned long flags;
>
> - return 0;
> + spin_lock_irqsave(&clocksource_lock, flags);
> + list_del(&cs->list);
> + if (clocksource_override == cs)
> + clocksource_override = NULL;
> + spin_unlock_irqrestore(&clocksource_lock, flags);
> }
>
> /**
> @@ -539,6 +533,25 @@ void clocksource_forward_now(void)
> }
>
> /**
> + * 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.
> + */
> +static struct clocksource *select_clocksource(void)
> +{
> + if (list_empty(&clocksource_list))
> + return NULL;
> +
> + if (clocksource_override)
> + return clocksource_override;
> +
> + return list_entry(clocksource_list.next, struct clocksource, list);
> +}
> +
> +/**
> * change_clocksource - Swaps clocksources if a new one is available
> *
> * Accumulates current time interval and initializes new clocksource
> @@ -577,6 +590,23 @@ void change_clocksource(void)
> clock->name);
> */
> }
> +
> +/**
> + * clocksource_update - Check if a better clocksource is available
> + */
> +static void clocksource_update(void)
> +{
> + struct clocksource *new;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&clocksource_lock, flags);
> + new = select_clocksource();
> + if (new)
> + next_clocksource = new;
> + spin_unlock_irqrestore(&clocksource_lock, flags);
> +}
> +#else /* CONFIG_GENERIC_TIME */
> +static inline void clocksource_update(void) { }
> #endif
>
> /**
> @@ -587,16 +617,13 @@ void change_clocksource(void)
> */
> int clocksource_register(struct clocksource *c)
> {
> - unsigned long flags;
> int ret;
>
> - spin_lock_irqsave(&clocksource_lock, flags);
> ret = clocksource_enqueue(c);
> - if (!ret)
> - next_clocksource = select_clocksource();
> - spin_unlock_irqrestore(&clocksource_lock, flags);
> - if (!ret)
> + if (!ret) {
> + clocksource_update();
> clocksource_check_watchdog(c);
> + }
> return ret;
> }
> EXPORT_SYMBOL(clocksource_register);
> @@ -607,14 +634,10 @@ EXPORT_SYMBOL(clocksource_register);
> */
> void clocksource_change_rating(struct clocksource *cs, int rating)
> {
> - unsigned long flags;
> -
> - spin_lock_irqsave(&clocksource_lock, flags);
> - list_del(&cs->list);
> + clocksource_dequeue(cs);
> cs->rating = rating;
> clocksource_enqueue(cs);
> - next_clocksource = select_clocksource();
> - spin_unlock_irqrestore(&clocksource_lock, flags);
> + clocksource_update();
> }
>
> /**
> @@ -622,14 +645,8 @@ void clocksource_change_rating(struct cl
> */
> void clocksource_unregister(struct clocksource *cs)
> {
> - unsigned long flags;
> -
> - spin_lock_irqsave(&clocksource_lock, flags);
> - list_del(&cs->list);
> - if (clocksource_override == cs)
> - clocksource_override = NULL;
> - next_clocksource = select_clocksource();
> - spin_unlock_irqrestore(&clocksource_lock, flags);
> + clocksource_dequeue(cs);
> + clocksource_update();
> }
>
> /**
> @@ -721,13 +738,13 @@ static ssize_t sysfs_override_clocksourc
> }
>
> /* Reselect, when the override name has changed */
> - if (ovr != clocksource_override) {
> + if (ovr != clocksource_override)
> clocksource_override = ovr;
> - next_clocksource = select_clocksource();
> - }
>
> spin_unlock_irq(&clocksource_lock);
>
> + clocksource_update();
> +
> return ret;
> }
>
>



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