linux-kernel - Re: [patch for 2.6.30 2/2] arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: avoid cross-CPU interrupts

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Message-Id: <1239431831.4418.22.camel@localhost.localdomain>
Date:	Sat, 11 Apr 2009 12:07:11 +0530
From:	Jaswinder Singh Rajput <jaswinder@...nel.org>
To:	akpm@...ux-foundation.org
Cc:	lenb@...nel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, davej@...hat.com, efault@....de,
	len.brown@...el.com, mingo@...e.hu, rusty@...tcorp.com.au,
	tglx@...utronix.de, venkatesh.pallipadi@...el.com,
	yakui.zhao@...el.com, yanmin_zhang@...ux.intel.com
Subject: Re: [patch for 2.6.30 2/2]
 arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: avoid cross-CPU interrupts

On Fri, 2009-04-10 at 23:17 -0700, akpm@...ux-foundation.org wrote:
> From: Andrew Morton <akpm@...ux-foundation.org>
> 
> In drv_read(), check to see whether we can run the rdmsr() on the current
> CPU.  If so, do that.  So smp_call_function_single() can avoid the IPI.
> 
> Arguably, cpumask_any() should do this.
> 
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Zhao Yakui <yakui.zhao@...el.com>
> Cc: Dave Jones <davej@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Mike Galbraith <efault@....de>
> Cc: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c |   17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff -puN arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-cross-cpu-interrupts arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
> --- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c~arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-cross-cpu-interrupts
> +++ a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
> @@ -197,9 +197,22 @@ static void do_drv_write(void *_cmd)
>  
>  static void drv_read(struct drv_cmd *cmd)
>  {
> -	cmd->val = 0;
> +	int target_cpu;		/* The CPU on which to perform thr rdmsr() */

+ 	int target_cpu; 	/* The CPU on which to perform the rdmsr() */

--
JSR

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