On Mon, 1 Jul 2013, Stephen Boyd wrote:
> On 07/01/13 10:49, Thomas Gleixner wrote:
> >
> > Though that does not explain why dev->next_event is set to KTIME_MAX
> > after we installed the mxc_timer1 as the system clocksource. And we
> > really need to know why that happens.
> >
> > Here is some more debugging which should shine some light on that.
>
> Each local_timer clockevent should have their next_event set for
> KTIME_MAX when they're registered because they get "shutdown" initially.
Yes.
> twd timers support both periodic and oneshot, so we won't emulate
> periodic mode with oneshot mode. Looking at tick_setup_periodic() it
> looks like the next_event member is ignored and we just set the mode to
> periodic. KTIME_MAX should still be there. That should be fine though as
> long as we don't switch the tick device into oneshot mode.
Correct.
> It seems that someone is switching the tick device into oneshot mode
> without changing the event handler away from tick_handle_periodic(). Is
> that supposed to happen? Most clockevents_set_mode(ONESHOT) calls are
> prefaced with a handler change or they're operating on the broadcast
> device. I suspect that tick_check_oneshot_broadcast() is the bad one.
> That one changes the mode and then tick_handle_periodic() probably runs
> past that if check and starts trying to emulate periodic mode when
> next_event is still KTIME_MAX.
The issue is very subtle. What happens is:
CPU0 CPU1
Switch to oneshot mode
Copy the bits from tick_broadcast_mask to
tick_broadcast_oneshot_mask. We need to do
that so the other cpus reach the timer irq
and the softirq which switches them to
oneshot.
Kick the broadcast device into oneshot.
Timer interrupt fires
irq_enter sees the cpu in
tick_broadcast_oneshot_mask and
sets the device to oneshot mode
handle_periodic:
Sees oneshot mode and adds
period to
dev->next_event(KTIME_MAX)
So we need two fixes:
1) The replacement of the dummy timer and the effect on the broadcast
mask/device
2) tick_check_oneshot_broadcast needs a sanity check
Patch below.
Thanks,
tglx
---
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 9d96a54..58d69eb 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -30,6 +30,7 @@
static struct tick_device tick_broadcast_device;
static cpumask_var_t tick_broadcast_mask;
+static cpumask_var_t tick_broadcast_on;
static cpumask_var_t tmpmask;
static DEFINE_RAW_SPINLOCK(tick_broadcast_lock);
static int tick_broadcast_force;
@@ -140,8 +141,9 @@ static void tick_device_setup_broadcast_func(struct
clock_event_device *dev)
*/
int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu)
{
+ struct clock_event_device *bc = tick_broadcast_device.evtdev;
unsigned long flags;
- int ret = 0;
+ int ret;
raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
@@ -155,22 +157,65 @@ int tick_device_uses_broadcast(struct clock_event_device
*dev, int cpu)
dev->event_handler = tick_handle_periodic;
tick_device_setup_broadcast_func(dev);
cpumask_set_cpu(cpu, tick_broadcast_mask);
- tick_broadcast_start_periodic(tick_broadcast_device.evtdev);
+ tick_broadcast_start_periodic(bc);
ret = 1;
} else {
+ int cpubc = cpumask_test_cpu(cpu, tick_broadcast_on);
+ int devc3 = dev->features & CLOCK_EVT_FEAT_C3STOP;
+
+ if (devc3)
+ tick_device_setup_broadcast_func(dev);
/*
- * When the new device is not affected by the stop
- * feature and the cpu is marked in the broadcast mask
- * then clear the broadcast bit.
+ * If broadcast mode is enforced, leave the broadcast
+ * mask alone.
*/
- if (!(dev->features & CLOCK_EVT_FEAT_C3STOP)) {
- int cpu = smp_processor_id();
- cpumask_clear_cpu(cpu, tick_broadcast_mask);
+ if (!tick_broadcast_force) {
+ /*
+ * Clear the broadcast bit for this cpu if the
+ * device is not powerstate affected or the
+ * cpu is not in the broadcast ON mode
+ */
+ if (!devc3 || !cpubc)
+ cpumask_clear_cpu(cpu, tick_broadcast_mask);
+ }
+
+ switch (tick_broadcast_device.mode) {
+ case TICKDEV_MODE_ONESHOT:
+ /*
+ * If the system is in oneshot mode we can
+ * unconditionally clear the oneshot mask,
+ * because the CPU is running and therefor not
+ * in an idle state which causes the C3
+ * affected device to stop. Let the caller
+ * initialize the device.
+ */
tick_broadcast_clear_oneshot(cpu);
- } else {
- tick_device_setup_broadcast_func(dev);
+ ret = 0;
+ break;
+
+ case TICKDEV_MODE_PERIODIC:
+ /*
+ * If the system is in periodic mode, check
+ * whether the broadcast device can be
+ * switched off now.
+ */
+ if (cpumask_empty(tick_broadcast_mask) && bc)
+ clockevents_shutdown(bc);
+ /*
+ * If we kept the cpu in the broadcast mask,
+ * tell the core code to leave it alone and
+ * leave the per cpu device in shutdown
+ * state.
+ */
+ ret = cpumask_test_cpu(cpu, tick_broadcast_mask);
+ break;
+ default:
+ /* Nothing to do */
+ ret = 0;
+ break;
}
}
+
raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
return ret;
}
@@ -298,6 +343,7 @@ static void tick_do_broadcast_on_off(unsigned long *reason)
switch (*reason) {
case CLOCK_EVT_NOTIFY_BROADCAST_ON:
case CLOCK_EVT_NOTIFY_BROADCAST_FORCE:
+ cpumask_set_cpu(cpu, tick_broadcast_on);
if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_mask)) {
if (tick_broadcast_device.mode ==
TICKDEV_MODE_PERIODIC)
@@ -307,8 +353,12 @@ static void tick_do_broadcast_on_off(unsigned long *reason)
tick_broadcast_force = 1;
break;
case CLOCK_EVT_NOTIFY_BROADCAST_OFF:
- if (!tick_broadcast_force &&
- cpumask_test_and_clear_cpu(cpu, tick_broadcast_mask)) {
+ if (tick_broadcast_force)
+ break;
+ cpumask_clear_cpu(cpu, tick_broadcast_on);
+ if (!tick_device_is_functional(dev))
+ break;
+ if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_mask)) {
if (tick_broadcast_device.mode ==
TICKDEV_MODE_PERIODIC)
tick_setup_periodic(dev, 0);
@@ -366,6 +416,7 @@ void tick_shutdown_broadcast(unsigned int *cpup)
bc = tick_broadcast_device.evtdev;
cpumask_clear_cpu(cpu, tick_broadcast_mask);
+ cpumask_clear_cpu(cpu, tick_broadcast_on);
if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) {
if (bc && cpumask_empty(tick_broadcast_mask))
@@ -492,7 +543,15 @@ void tick_check_oneshot_broadcast(int cpu)
if (cpumask_test_cpu(cpu, tick_broadcast_oneshot_mask)) {
struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
- clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_ONESHOT);
+ /*
+ * We might be in the middle of switching over from
+ * periodic to oneshot. If the CPU has not yet
+ * switched over, leave the device alone.
+ */
+ if (td->mode == TICKDEV_MODE_ONESHOT) {
+ clockevents_set_mode(td->evtdev,
+ CLOCK_EVT_MODE_ONESHOT);
+ }
}
}
@@ -809,6 +868,7 @@ bool tick_broadcast_oneshot_available(void)
void __init tick_broadcast_init(void)
{
zalloc_cpumask_var(&tick_broadcast_mask, GFP_NOWAIT);
+ zalloc_cpumask_var(&tick_broadcast_on, GFP_NOWAIT);
zalloc_cpumask_var(&tmpmask, GFP_NOWAIT);
#ifdef CONFIG_TICK_ONESHOT
zalloc_cpumask_var(&tick_broadcast_oneshot_mask, GFP_NOWAIT);
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index edd45f6..5e3ed78 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -194,7 +194,8 @@ static void tick_setup_device(struct tick_device *td,
* When global broadcasting is active, check if the current
* device is registered as a placeholder for broadcast mode.
* This allows us to handle this x86 misfeature in a generic
- * way.
+ * way. This function also returns !=0 when we keep the
+ * current active broadcast state.
*/
if (tick_device_uses_broadcast(newdev, cpu))
return;
--
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