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[PATCH 2/2] xen/events: Convert to hotplug state machine

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  [PATCH 2/2] xen/events: Convert to hotplug state machine Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-08-15 16:40 +0200
    Re: [Xen-devel] [PATCH 2/2] xen/events: Convert to hotplug state  machine David Vrabel <david.vrabel@citrix.com> - 2016-08-15 17:10 +0200
      Re: [Xen-devel] [PATCH 2/2] xen/events: Convert to hotplug state  machine Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-08-15 18:00 +0200

#1462832 — [PATCH 2/2] xen/events: Convert to hotplug state machine

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Install the callbacks via the state machine.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
Changes from Sebastian's original version:
* Renamed hotplug state from CPUHP_XEN_EV_PREPEARE to CPUHP_XEN_EVTCHN_PREPARE
* Dropped suggestion in the commit messages about moving evtchn_fifo_alloc_control_block
  call since I think it is in the right place right now.


 drivers/xen/events/events_fifo.c |   34 ++++++++++++----------------------
 include/linux/cpuhotplug.h       |    1 +
 2 files changed, 13 insertions(+), 22 deletions(-)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 266c2c7..7ef27c6 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -418,30 +418,18 @@ static int evtchn_fifo_alloc_control_block(unsigned cpu)
 	return ret;
 }
 
-static int evtchn_fifo_cpu_notification(struct notifier_block *self,
-						  unsigned long action,
-						  void *hcpu)
+static int xen_evtchn_cpu_prepare(unsigned int cpu)
 {
-	int cpu = (long)hcpu;
-	int ret = 0;
-
-	switch (action) {
-	case CPU_UP_PREPARE:
-		if (!per_cpu(cpu_control_block, cpu))
-			ret = evtchn_fifo_alloc_control_block(cpu);
-		break;
-	case CPU_DEAD:
-		__evtchn_fifo_handle_events(cpu, true);
-		break;
-	default:
-		break;
-	}
-	return ret < 0 ? NOTIFY_BAD : NOTIFY_OK;
+	if (!per_cpu(cpu_control_block, cpu))
+		return evtchn_fifo_alloc_control_block(cpu);
+	return 0;
 }
 
-static struct notifier_block evtchn_fifo_cpu_notifier = {
-	.notifier_call	= evtchn_fifo_cpu_notification,
-};
+static int xen_evtchn_cpu_dead(unsigned int cpu)
+{
+	__evtchn_fifo_handle_events(cpu, true);
+	return 0;
+}
 
 int __init xen_evtchn_fifo_init(void)
 {
@@ -456,7 +444,9 @@ int __init xen_evtchn_fifo_init(void)
 
 	evtchn_ops = &evtchn_ops_fifo;
 
-	register_cpu_notifier(&evtchn_fifo_cpu_notifier);
+	cpuhp_setup_state_nocalls(CPUHP_XEN_EVTCHN_PREPARE,
+				  "CPUHP_XEN_EVTCHN_PREPARE",
+				  xen_evtchn_cpu_prepare, xen_evtchn_cpu_dead);
 out:
 	put_cpu();
 	return ret;
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index d6beeb9..c60a17c 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -22,6 +22,7 @@ enum cpuhp_state {
 	CPUHP_SMPCFD_PREPARE,
 	CPUHP_RCUTREE_PREP,
 	CPUHP_XEN_PREPARE,
+	CPUHP_XEN_EVTCHN_PREPARE,
 	CPUHP_NOTIFY_PREPARE,
 	CPUHP_TIMERS_DEAD,
 	CPUHP_BRINGUP_CPU,
-- 
1.7.1

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#1462876 — Re: [Xen-devel] [PATCH 2/2] xen/events: Convert to hotplug state machine

On 15/08/16 15:46, Boris Ostrovsky wrote:
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> Install the callbacks via the state machine.
[...]
> +static int xen_evtchn_cpu_dead(unsigned int cpu)
> +{
> +	__evtchn_fifo_handle_events(cpu, true);
> +	return 0;
> +}

I'm not familiar with the new state machine.  When this is called, what
state is the CPU in?

In particular, local interrupts must be disabled and all non-percpu irqs
must have been migrated to other CPUs.


>  int __init xen_evtchn_fifo_init(void)
>  {
> @@ -456,7 +444,9 @@ int __init xen_evtchn_fifo_init(void)
>  
>  	evtchn_ops = &evtchn_ops_fifo;
>  
> -	register_cpu_notifier(&evtchn_fifo_cpu_notifier);
> +	cpuhp_setup_state_nocalls(CPUHP_XEN_EVTCHN_PREPARE,
> +				  "CPUHP_XEN_EVTCHN_PREPARE",
> +				  xen_evtchn_cpu_prepare, xen_evtchn_cpu_dead);
>  out:
>  	put_cpu();
>  	return ret;
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index d6beeb9..c60a17c 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -22,6 +22,7 @@ enum cpuhp_state {
>  	CPUHP_SMPCFD_PREPARE,
>  	CPUHP_RCUTREE_PREP,
>  	CPUHP_XEN_PREPARE,
> +	CPUHP_XEN_EVTCHN_PREPARE,
>  	CPUHP_NOTIFY_PREPARE,
>  	CPUHP_TIMERS_DEAD,
>  	CPUHP_BRINGUP_CPU,
> 

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#1462953 — Re: [Xen-devel] [PATCH 2/2] xen/events: Convert to hotplug state machine

On 08/15/2016 11:06 AM, David Vrabel wrote:
> On 15/08/16 15:46, Boris Ostrovsky wrote:
>> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>>
>> Install the callbacks via the state machine.
> [...]
>> +static int xen_evtchn_cpu_dead(unsigned int cpu)
>> +{
>> +	__evtchn_fifo_handle_events(cpu, true);
>> +	return 0;
>> +}
> I'm not familiar with the new state machine.  When this is called, what
> state is the CPU in?
>
> In particular, local interrupts must be disabled and all non-percpu irqs
> must have been migrated to other CPUs.

This (xen_evtchn_cpu_dead()) is called immediately after notify_dead()
on the way down.

The state machine is walking cpuhp_state list and for each member of the
list it calls the callback that has been registered for that member.

So when we bring a CPU up first we call xen_evtchn_cpu_prepare() and
then in the next iteration of the state machine loop notify_prepare()
(because CPUHP_XEN_EVTCHN_PREPARE is immediately before
CPUHP_NOTIFY_PREPARE). On the way down it's done in reverse: first
notify_dead() and then xen_evtchn_cpu_dead().

In other words, the old notification scheme is part of new state machine:

	CPUHP_RCUTREE_PREP,
 	CPUHP_XEN_PREPARE,
+	CPUHP_XEN_EVTCHN_PREPARE,
 	CPUHP_NOTIFY_PREPARE,  <=== CPU notifiers callback
	CPUHP_TIMERS_DEAD,
	CPUHP_BRINGUP_CPU,


-boris


>
>
>>  int __init xen_evtchn_fifo_init(void)
>>  {
>> @@ -456,7 +444,9 @@ int __init xen_evtchn_fifo_init(void)
>>  
>>  	evtchn_ops = &evtchn_ops_fifo;
>>  
>> -	register_cpu_notifier(&evtchn_fifo_cpu_notifier);
>> +	cpuhp_setup_state_nocalls(CPUHP_XEN_EVTCHN_PREPARE,
>> +				  "CPUHP_XEN_EVTCHN_PREPARE",
>> +				  xen_evtchn_cpu_prepare, xen_evtchn_cpu_dead);
>>  out:
>>  	put_cpu();
>>  	return ret;
>> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
>> index d6beeb9..c60a17c 100644
>> --- a/include/linux/cpuhotplug.h
>> +++ b/include/linux/cpuhotplug.h
>> @@ -22,6 +22,7 @@ enum cpuhp_state {
>>  	CPUHP_SMPCFD_PREPARE,
>>  	CPUHP_RCUTREE_PREP,
>>  	CPUHP_XEN_PREPARE,
>> +	CPUHP_XEN_EVTCHN_PREPARE,
>>  	CPUHP_NOTIFY_PREPARE,
>>  	CPUHP_TIMERS_DEAD,
>>  	CPUHP_BRINGUP_CPU,
>>

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