So with the patch I get the following jitter:
reported res = 0.000001000
starting calibrate
finished calibrate: 367.9363MHz 367936300
Requested timex Max Min error
--------------- --- --- -----
0.000001000 0.000018185 0.000003998 0.000017185 (17.185 usecs)
0.000010000 0.000021381 0.000018278 0.000011381 (11.381 usecs)
0.000100000 0.000109614 0.000108443 0.000009614 (9.614 usecs)
The jitter test can be found here:
http://www.kihontech.com/tests/hrtimer/jitter_inc.c
10 consecutive runs of the jitter test without the patch.
http://www.kihontech.com/tests/hrtimer/jitter_nopatch.txt
10 consecutive runs of the jitter test with the patch.
http://www.kihontech.com/tests/hrtimer/jitter_patch.txt
I'll be adding this patch to my 2.6.15-rt1-sr2 patch to be released soon.
-- Steve
Index: linux-2.6.15-rt1/kernel/hrtimer.c
===================================================================
--- linux-2.6.15-rt1.orig/kernel/hrtimer.c 2006-01-03 07:41:48.000000000 -0500
+++ linux-2.6.15-rt1/kernel/hrtimer.c 2006-01-05 22:17:45.000000000 -0500
@@ -226,6 +226,10 @@
* for which the hrt time source was armed.
*
* Called with interrupts disabled and base lock held
+ *
+ * Returns:
+ * 0 on success
+ * 1 if time has already past.
*/
static int hrtimer_reprogram(struct hrtimer *timer, struct hrtimer_base *base)
{
@@ -239,6 +243,8 @@
res = clockevents_set_next_event(expires);
if (!res)
*expires_next = expires;
+ else
+ res = 1;
return res;
}
@@ -381,11 +387,24 @@
smp_processor_id());
}
+/*
+ * kick_off_hrtimer - queue the timer to the expire list and
+ * raise the hrtimer softirq.
+ */
+static inline void
+kick_off_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
+{
+ list_add_tail(&timer->list, &base->expired);
+ timer->state = HRTIMER_PENDING_CALLBACK;
+ raise_softirq(HRTIMER_SOFTIRQ);
+}
+
#else /* CONFIG_HIGH_RES_TIMERS */
# define hrtimer_hres_active 0
# define hres_enqueue_expired(t,b,n) 0
# define hrtimer_check_clocks() do { } while (0)
+# define kick_off_hrtimer do { } while (0)
#endif /* !CONFIG_HIGH_RES_TIMERS */
@@ -501,8 +520,12 @@
*
* The timer is inserted in expiry order. Insertion into the
* red black tree is O(log(n)). Must hold the base lock.
+ *
+ * Returns:
+ * 0 on success
+ * 1 if time has already past.
*/
-static void enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
+static int enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
{
struct rb_node **link = &base->active.rb_node;
struct rb_node *parent = NULL;
@@ -534,12 +557,8 @@
* past we just move it to the expired list
* and schedule the softirq.
*/
- if (hrtimer_hres_active && hrtimer_reprogram(timer, base)) {
- list_add_tail(&timer->list, &base->expired);
- timer->state = HRTIMER_PENDING_CALLBACK;
- raise_softirq(HRTIMER_SOFTIRQ);
- return;
- }
+ if (hrtimer_hres_active && hrtimer_reprogram(timer, base))
+ return 1;
#endif
base->first = &timer->node;
}
@@ -551,6 +570,7 @@
rb_insert_color(&timer->node, &base->active);
timer->state = HRTIMER_PENDING;
+ return 0;
}
/*
@@ -598,7 +618,7 @@
*
* Returns:
* 0 on success
- * 1 when the timer was active
+ * 1 if the time has already past
*/
int
hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
@@ -610,7 +630,7 @@
base = lock_hrtimer_base(timer, &flags);
/* Remove an active timer from the queue: */
- ret = remove_hrtimer(timer, base);
+ remove_hrtimer(timer, base);
/* Switch the timer base, if necessary: */
new_base = switch_hrtimer_base(timer, base);
@@ -619,7 +639,7 @@
tim = ktime_add(tim, new_base->get_time());
timer->expires = tim;
- enqueue_hrtimer(timer, new_base);
+ ret = enqueue_hrtimer(timer, new_base);
unlock_hrtimer_base(timer, &flags);
@@ -864,9 +884,10 @@
spin_lock_irq(&base->lock);
- if (restart == HRTIMER_RESTART)
- enqueue_hrtimer(timer, base);
- else
+ if (restart == HRTIMER_RESTART) {
+ if (enqueue_hrtimer(timer, base))
+ kick_off_hrtimer(timer, base);
+ } else
timer->state = HRTIMER_EXPIRED;
set_curr_timer(base, NULL);
}
@@ -922,9 +943,10 @@
spin_lock_irq(&base->lock);
- if (restart == HRTIMER_RESTART)
- enqueue_hrtimer(timer, base);
- else
+ if (restart == HRTIMER_RESTART) {
+ if (enqueue_hrtimer(timer, base))
+ kick_off_hrtimer(timer, base);
+ } else
timer->state = HRTIMER_EXPIRED;
set_curr_timer(base, NULL);
}
@@ -983,9 +1005,13 @@
/* fn stays NULL, meaning single-shot wakeup: */
timer->data = current;
- hrtimer_start(timer, timer->expires, mode);
+ if (hrtimer_start(timer, timer->expires, mode)) {
+ /* time already past */
+ timer->state = HRTIMER_EXPIRED;
+ set_current_state(TASK_RUNNING);
+ } else
+ schedule();
- schedule();
hrtimer_cancel(timer);
/* Return the remaining time: */
@@ -1128,7 +1154,8 @@
timer = rb_entry(node, struct hrtimer, node);
__remove_hrtimer(timer, old_base);
timer->base = new_base;
- enqueue_hrtimer(timer, new_base);
+ if (enqueue_hrtimer(timer, new_base))
+ kick_off_hrtimer(timer, base);
}
}
-
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