linux-kernel - Re: [RESEND PATCH 2/2] perf, cpu hotplug: Use cached value of smp_processor

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Date:	Tue, 16 Oct 2012 09:32:11 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...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 2/2] perf, cpu hotplug: Use cached value of
 smp_processor_id()

On Tue, Oct 16, 2012 at 01:28:17PM +0530, Srivatsa S. Bhat wrote:
> The perf_cpu_notifier() macro invokes smp_processor_id() multiple
> times. Optimize it by using a local variable.
> 
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
> 
>  include/linux/perf_event.h |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 0647805..6bfb2faa 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -803,15 +803,16 @@ 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 cpu = smp_processor_id();				\
>  	unsigned long flags;						\
>  	fn(&fn##_nb, (unsigned long)CPU_UP_PREPARE,			\
> -		(void *)(unsigned long)smp_processor_id());		\
> +		(void *)(unsigned long)cpu);				\
>  	local_irq_save(flags);						\
>  	fn(&fn##_nb, (unsigned long)CPU_STARTING,			\
> -		(void *)(unsigned long)smp_processor_id());		\
> +		(void *)(unsigned long)cpu);				\
>  	local_irq_restore(flags);					\
>  	fn(&fn##_nb, (unsigned long)CPU_ONLINE,				\
> -		(void *)(unsigned long)smp_processor_id());		\
> +		(void *)(unsigned long)cpu);				\
>  	register_cpu_notifier(&fn##_nb);				\
>  } while (0)
> 
> 

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