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

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Message-ID: <507D8D3B.5000506@linux.vnet.ibm.com>
Date:	Tue, 16 Oct 2012 22:07:15 +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 10/16/2012 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() :-)

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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