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SubjectRe: [v4 RFC PATCH 4/4] timers: logic to move non pinned timers
* Arun R Bharadwaj <arun@linux.vnet.ibm.com> [2009-04-01 17:07:38]:

--------snip--------------
> Index: linux.trees.git/include/linux/hrtimer.h
> ===================================================================
> --- linux.trees.git.orig/include/linux/hrtimer.h
> +++ linux.trees.git/include/linux/hrtimer.h
> @@ -22,7 +22,6 @@
> #include <linux/wait.h>
> #include <linux/percpu.h>
>
> -
> struct hrtimer_clock_base;
> struct hrtimer_cpu_base;
>
> @@ -376,6 +375,24 @@ extern ktime_t hrtimer_get_remaining(con
> extern int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp);
>
> extern ktime_t hrtimer_get_next_event(void);
> +extern ktime_t hrtimer_get_next_event_on(int cpu);
> +
> +#define TICK_PERIOD_IN_NS NSEC_PER_SEC / HZ
> +/*
> + * Helper function to check before migrating a hrtimer if it expires
> + * before the next timer interrupt on the target cpu.
> + */
> +static inline int check_hrtimer_latency(struct hrtimer *timer, int cpu)
> +{
> + unsigned long next_hrtimeout, next_jiffies;
> + next_jiffies = get_next_timer_interrupt_on(jiffies, cpu);
> + next_jiffies = next_jiffies * TICK_PERIOD_IN_NS;
> + next_hrtimeout = hrtimer_get_expires_ns(timer);
> +
> + if (next_hrtimeout > next_jiffies)
> + return 1;
> + return 0;
> +}
>

This function can be greatly simplified.
Here i am getting the next timer interrupt on target_cpu.
The target_cpu is the idle load balancer.
So we can check if the hrtimer expiry is before the next tick
on the ilb or not.
By doing this we can eliminate a lot of extra code, which would
otherwise be needed in the form of helper functions for
get_next_timer_interrupt_on().

After simplification the code would simply look like
static inline int check_hrtimer_latency(struct hrtimer *timer, int cpu)
{
unsigned long next_hrtimeout, next_jiffies;
next_jiffies = (jiffies + 1) * TICK_PERIOD_IN_NS;
next_hrtimeout = hrtimer_get_expires_ns(timer);

if(.....)
}
--arun

> /*
> * A timer is active, when it is enqueued into the rbtree or the callback
> Index: linux.trees.git/include/linux/timer.h
> ===================================================================
> --- linux.trees.git.orig/include/linux/timer.h
> +++ linux.trees.git/include/linux/timer.h
> @@ -184,7 +184,7 @@ extern unsigned long next_timer_interrup
> * jiffie.
> */
> extern unsigned long get_next_timer_interrupt(unsigned long now);
> -
> +extern unsigned long get_next_timer_interrupt_on(unsigned long now, int cpu);
> /*
> * Timer-statistics info:
> */


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