linux-kernel - Re: [RESEND PATCH 1/2] perf, cpu hotplug: Run CPU

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Message-ID: <507E388F.102@linux.vnet.ibm.com>
Date:	Wed, 17 Oct 2012 10:18:15 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	peterz@...radead.org, acme@...stprotocols.net, mingo@...nel.org,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH 1/2] perf, cpu hotplug: Run CPU_STARTING notifiers
 with irqs disabled

On 10/17/2012 12:04 AM, Paul E. McKenney wrote:
> On Tue, Oct 16, 2012 at 10:07:15PM +0530, Srivatsa S. Bhat wrote:
>> On 10/16/2012 10:01 PM, Paul E. McKenney wrote:
>>> On Tue, Oct 16, 2012 at 01:28:10PM +0530, Srivatsa S. Bhat wrote:
>>>> The CPU_STARTING notifiers are supposed to be run with irqs disabled. But the
>>>> perf_cpu_notifier() macro invokes them without doing that. Fix it.
>>>
>>> Color me confused...
>>
>> Hehe, I believe the context provided by diff tricked you ;-)
>> The function I am referring to is perf_cpu_notifier(), not
>> perf_event_task_tick() :-)
> 
> It did indeed fool me!  And indeed, checking the code did indeed show
> that the name of interest if perf_cpu_notifier().
> 
> When using the correct name, I do indeed find places where it is
> called with interrupts enabled.  So...
> 
> Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>

Great! Thank you :)

Regards,
Srivatsa S. Bhat

>>
>>>  Isn't perf_event_task_tick() invoked only
>>> from scheduler_tick(), which always has interrupts disabled?
>>>
>>> Or are you needing to invoke it from somewhere else?
>>>
>>> 							Thanx, Paul
>>>
>>>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
>>>> ---
>>>>
>>>>  include/linux/perf_event.h |    3 +++
>>>>  1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>>>> index 2e90235..0647805 100644
>>>> --- a/include/linux/perf_event.h
>>>> +++ b/include/linux/perf_event.h
>>>> @@ -803,10 +803,13 @@ static inline void perf_event_task_tick(void)				{ }
>>>>  do {									\
>>>>  	static struct notifier_block fn##_nb __cpuinitdata =		\
>>>>  		{ .notifier_call = fn, .priority = CPU_PRI_PERF };	\
>>>> +	unsigned long flags;						\
>>>>  	fn(&fn##_nb, (unsigned long)CPU_UP_PREPARE,			\
>>>>  		(void *)(unsigned long)smp_processor_id());		\
>>>> +	local_irq_save(flags);						\
>>>>  	fn(&fn##_nb, (unsigned long)CPU_STARTING,			\
>>>>  		(void *)(unsigned long)smp_processor_id());		\
>>>> +	local_irq_restore(flags);					\
>>>>  	fn(&fn##_nb, (unsigned long)CPU_ONLINE,				\
>>>>  		(void *)(unsigned long)smp_processor_id());		\
>>>>  	register_cpu_notifier(&fn##_nb);				\
>>>>
>>

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