Re: [PATCH] trace: use __this_cpu_inc/dec operation instead of __get_cpu_var

[Shan Wei]

ping ......


Shan Wei said, at 2012/11/19 13:21:
> From: Shan Wei <davidshan@xxxxxxxxxxx>
> 
> __this_cpu_inc_return() or __this_cpu_dec generates a single instruction,
> which is faster than __get_cpu_var operation.
> 
> Signed-off-by: Shan Wei <davidshan@xxxxxxxxxxx>
> ---
>  kernel/trace/trace.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 18c0aa8..3795694 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1313,7 +1313,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
>  	 */
>  	preempt_disable_notrace();
>  
> -	use_stack = ++__get_cpu_var(ftrace_stack_reserve);
> +	use_stack = __this_cpu_inc_return(ftrace_stack_reserve);
>  	/*
>  	 * We don't need any atomic variables, just a barrier.
>  	 * If an interrupt comes in, we don't care, because it would
> @@ -1367,7 +1367,7 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
>   out:
>  	/* Again, don't let gcc optimize things here */
>  	barrier();
> -	__get_cpu_var(ftrace_stack_reserve)--;
> +	__this_cpu_dec(ftrace_stack_reserve);
>  	preempt_enable_notrace();
>  
>  }
> 

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