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Subject[PATCH 05/13] hrtimer: optimize hrtimer_run_queues

Every time hrtimer_run_queues() is called, get_time() is called twice,
which can be quite expensive, just reading xtime is much cheaper and
does the same job (at least for the current low resolution timer, for
high resolution timer we can something different later).
Cache the expiry time in last_expired, so run_hrtimer_queue() doesn't
has to calculate it (clock sources usually know when their expired).

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>

---
include/linux/hrtimer.h | 1 +
kernel/hrtimer.c | 17 +++++++++++++----
2 files changed, 14 insertions(+), 4 deletions(-)
Index: linux-2.6-git/include/linux/hrtimer.h
===================================================================
--- linux-2.6-git.orig/include/linux/hrtimer.h 2006-02-12 18:33:07.000000000 +0100
+++ linux-2.6-git/include/linux/hrtimer.h 2006-02-12 18:33:21.000000000 +0100
@@ -89,6 +89,7 @@ struct hrtimer_base {
ktime_t resolution;
ktime_t (*get_time)(void);
struct hrtimer *curr_timer;
+ ktime_t last_expired;
};

/*
Index: linux-2.6-git/kernel/hrtimer.c
===================================================================
--- linux-2.6-git.orig/kernel/hrtimer.c 2006-02-12 18:33:16.000000000 +0100
+++ linux-2.6-git/kernel/hrtimer.c 2006-02-12 18:33:21.000000000 +0100
@@ -541,7 +541,7 @@ int hrtimer_get_res(clockid_t which_cloc
*/
static inline void run_hrtimer_queue(struct hrtimer_base *base)
{
- ktime_t now = base->get_time();
+ ktime_t now = base->last_expired;
struct rb_node *node;

spin_lock_irq(&base->lock);
@@ -594,10 +594,19 @@ static inline void run_hrtimer_queue(str
void hrtimer_run_queues(void)
{
struct hrtimer_base *base = __get_cpu_var(hrtimer_bases);
- int i;
+ ktime_t now, mono;
+ int seq;

- for (i = 0; i < MAX_HRTIMER_BASES; i++)
- run_hrtimer_queue(&base[i]);
+ do {
+ seq = read_seqbegin(&xtime_lock);
+ now = timespec_to_ktime(xtime);
+ mono = timespec_to_ktime(wall_to_monotonic);
+ } while (read_seqretry(&xtime_lock, seq));
+
+ base[CLOCK_REALTIME].last_expired = now;
+ run_hrtimer_queue(&base[CLOCK_REALTIME]);
+ base[CLOCK_MONOTONIC].last_expired = ktime_add(now, mono);
+ run_hrtimer_queue(&base[CLOCK_MONOTONIC]);
}

/*
-
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