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Date: Tue, 14 Jul 2009 17:56:02 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [GIT pull] timer fixes for 2.6.31
Linus,
Please pull the latest timers-fixes-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git timers-fixes-for-linus
Thanks,
tglx
------------------>
Heiko Carstens (1):
timer stats: fix quick check optimization
Thomas Gleixner (2):
hrtimer: migration: do not check expiry time on current CPU
hrtimer: Fix migration expiry check
include/linux/clockchips.h | 9 ----
include/linux/hrtimer.h | 2 +-
kernel/hrtimer.c | 110 +++++++++++++++++++++++++------------------
kernel/time/clockevents.c | 11 ----
4 files changed, 65 insertions(+), 67 deletions(-)
diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 20a100f..3a1dbba 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -143,12 +143,3 @@ extern void clockevents_notify(unsigned long reason, void *arg);
#endif
#endif
-
-#ifdef CONFIG_GENERIC_CLOCKEVENTS
-extern ktime_t clockevents_get_next_event(int cpu);
-#else
-static inline ktime_t clockevents_get_next_event(int cpu)
-{
- return (ktime_t) { .tv64 = KTIME_MAX };
-}
-#endif
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 54648e6..4759917 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -448,7 +448,7 @@ extern void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
static inline void timer_stats_account_hrtimer(struct hrtimer *timer)
{
- if (likely(!timer->start_pid))
+ if (likely(!timer->start_site))
return;
timer_stats_update_stats(timer, timer->start_pid, timer->start_site,
timer->function, timer->start_comm, 0);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 9002958..49da79a 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -191,6 +191,46 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
}
}
+
+/*
+ * Get the preferred target CPU for NOHZ
+ */
+static int hrtimer_get_target(int this_cpu, int pinned)
+{
+#ifdef CONFIG_NO_HZ
+ if (!pinned && get_sysctl_timer_migration() && idle_cpu(this_cpu)) {
+ int preferred_cpu = get_nohz_load_balancer();
+
+ if (preferred_cpu >= 0)
+ return preferred_cpu;
+ }
+#endif
+ return this_cpu;
+}
+
+/*
+ * With HIGHRES=y we do not migrate the timer when it is expiring
+ * before the next event on the target cpu because we cannot reprogram
+ * the target cpu hardware and we would cause it to fire late.
+ *
+ * Called with cpu_base->lock of target cpu held.
+ */
+static int
+hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
+{
+#ifdef CONFIG_HIGH_RES_TIMERS
+ ktime_t expires;
+
+ if (!new_base->cpu_base->hres_active)
+ return 0;
+
+ expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);
+ return expires.tv64 <= new_base->cpu_base->expires_next.tv64;
+#else
+ return 0;
+#endif
+}
+
/*
* Switch the timer base to the current CPU when possible.
*/
@@ -200,16 +240,8 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
{
struct hrtimer_clock_base *new_base;
struct hrtimer_cpu_base *new_cpu_base;
- int cpu, preferred_cpu = -1;
-
- cpu = smp_processor_id();
-#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
- if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu)) {
- preferred_cpu = get_nohz_load_balancer();
- if (preferred_cpu >= 0)
- cpu = preferred_cpu;
- }
-#endif
+ int this_cpu = smp_processor_id();
+ int cpu = hrtimer_get_target(this_cpu, pinned);
again:
new_cpu_base = &per_cpu(hrtimer_bases, cpu);
@@ -217,7 +249,7 @@ again:
if (base != new_base) {
/*
- * We are trying to schedule the timer on the local CPU.
+ * We are trying to move timer to new_base.
* However we can't change timer's base while it is running,
* so we keep it on the same CPU. No hassle vs. reprogramming
* the event source in the high resolution case. The softirq
@@ -233,38 +265,12 @@ again:
spin_unlock(&base->cpu_base->lock);
spin_lock(&new_base->cpu_base->lock);
- /* Optimized away for NOHZ=n SMP=n */
- if (cpu == preferred_cpu) {
- /* Calculate clock monotonic expiry time */
-#ifdef CONFIG_HIGH_RES_TIMERS
- ktime_t expires = ktime_sub(hrtimer_get_expires(timer),
- new_base->offset);
-#else
- ktime_t expires = hrtimer_get_expires(timer);
-#endif
-
- /*
- * Get the next event on target cpu from the
- * clock events layer.
- * This covers the highres=off nohz=on case as well.
- */
- ktime_t next = clockevents_get_next_event(cpu);
-
- ktime_t delta = ktime_sub(expires, next);
-
- /*
- * We do not migrate the timer when it is expiring
- * before the next event on the target cpu because
- * we cannot reprogram the target cpu hardware and
- * we would cause it to fire late.
- */
- if (delta.tv64 < 0) {
- cpu = smp_processor_id();
- spin_unlock(&new_base->cpu_base->lock);
- spin_lock(&base->cpu_base->lock);
- timer->base = base;
- goto again;
- }
+ if (cpu != this_cpu && hrtimer_check_target(timer, new_base)) {
+ cpu = this_cpu;
+ spin_unlock(&new_base->cpu_base->lock);
+ spin_lock(&base->cpu_base->lock);
+ timer->base = base;
+ goto again;
}
timer->base = new_base;
}
@@ -1276,14 +1282,22 @@ void hrtimer_interrupt(struct clock_event_device *dev)
expires_next.tv64 = KTIME_MAX;
+ spin_lock(&cpu_base->lock);
+ /*
+ * We set expires_next to KTIME_MAX here with cpu_base->lock
+ * held to prevent that a timer is enqueued in our queue via
+ * the migration code. This does not affect enqueueing of
+ * timers which run their callback and need to be requeued on
+ * this CPU.
+ */
+ cpu_base->expires_next.tv64 = KTIME_MAX;
+
base = cpu_base->clock_base;
for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
ktime_t basenow;
struct rb_node *node;
- spin_lock(&cpu_base->lock);
-
basenow = ktime_add(now, base->offset);
while ((node = base->first)) {
@@ -1316,11 +1330,15 @@ void hrtimer_interrupt(struct clock_event_device *dev)
__run_hrtimer(timer);
}
- spin_unlock(&cpu_base->lock);
base++;
}
+ /*
+ * Store the new expiry value so the migration code can verify
+ * against it.
+ */
cpu_base->expires_next = expires_next;
+ spin_unlock(&cpu_base->lock);
/* Reprogramming necessary ? */
if (expires_next.tv64 != KTIME_MAX) {
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 1ad6dd4..a6dcd67 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -254,15 +254,4 @@ void clockevents_notify(unsigned long reason, void *arg)
spin_unlock(&clockevents_lock);
}
EXPORT_SYMBOL_GPL(clockevents_notify);
-
-ktime_t clockevents_get_next_event(int cpu)
-{
- struct tick_device *td;
- struct clock_event_device *dev;
-
- td = &per_cpu(tick_cpu_device, cpu);
- dev = td->evtdev;
-
- return dev->next_event;
-}
#endif
--
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