linux-kernel - Re: x86: use this_cpu for debug_stack

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Date:	Tue, 06 Aug 2013 15:02:45 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Christoph Lameter <cl@...two.org>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: x86: use this_cpu for debug_stack_usage

On Tue, 2013-08-06 at 18:56 +0000, Christoph Lameter wrote:
> > Might as well change is_debug_stack() to use __this_cpu_read() instead
> > of __get_cpu_var().

I just noticed that you didn't include the x86 maintainers.

Reviewed-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> 
> 
> 
> 
> 
> Subject: x86: use this_cpu for debug_stack_usage
> 
> Reduces overhead a bit and frees up a couple of registers.
> 
> Signed-off-by: Christoph Lameter <cl@...ux.com>
> 
> Index: linux/arch/x86/include/asm/debugreg.h
> ===================================================================
> --- linux.orig/arch/x86/include/asm/debugreg.h	2013-08-06 13:52:23.740092873 -0500
> +++ linux/arch/x86/include/asm/debugreg.h	2013-08-06 13:52:23.740092873 -0500
> @@ -97,11 +97,11 @@ extern void hw_breakpoint_restore(void);
>  DECLARE_PER_CPU(int, debug_stack_usage);
>  static inline void debug_stack_usage_inc(void)
>  {
> -	__get_cpu_var(debug_stack_usage)++;
> +	__this_cpu_inc(debug_stack_usage);
>  }
>  static inline void debug_stack_usage_dec(void)
>  {
> -	__get_cpu_var(debug_stack_usage)--;
> +	__this_cpu_dec(debug_stack_usage);
>  }
>  int is_debug_stack(unsigned long addr);
>  void debug_stack_set_zero(void);
> Index: linux/arch/x86/kernel/cpu/common.c
> ===================================================================
> --- linux.orig/arch/x86/kernel/cpu/common.c	2013-07-19 09:06:36.850047837 -0500
> +++ linux/arch/x86/kernel/cpu/common.c	2013-08-06 13:54:36.426384889 -0500
> @@ -1144,9 +1144,9 @@ DEFINE_PER_CPU(int, debug_stack_usage);
> 
>  int is_debug_stack(unsigned long addr)
>  {
> -	return __get_cpu_var(debug_stack_usage) ||
> -		(addr <= __get_cpu_var(debug_stack_addr) &&
> -		 addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ));
> +	return __this_cpu_read(debug_stack_usage) ||
> +		(addr <= __this_cpu_read(debug_stack_addr) &&
> +		 addr > (__this_cpu_read(debug_stack_addr) - DEBUG_STKSZ));
>  }
> 
>  DEFINE_PER_CPU(u32, debug_idt_ctr);


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