linux-kernel - Re: [PATCH] x86: printk_time to use tsc before cpu

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Date:	Tue, 29 Jul 2008 12:13:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: printk_time to use tsc before cpu_clock is ready

On Tue, 2008-07-29 at 03:09 -0700, Yinghai Lu wrote:
> so can get tsc value on printk
> 
> need to apply after
> 	[PATCH] printk_time: prepare stub for using other than cpu_clock


You failed to mention why we want this... ;-)


> Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>
> 
> ---
>  arch/x86/kernel/cpu/common.c    |   11 +++++++++++
>  arch/x86/kernel/cpu/common_64.c |   12 ++++++++++++
>  2 files changed, 23 insertions(+)
> 
> Index: linux-2.6/arch/x86/kernel/cpu/common.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/common.c
> +++ linux-2.6/arch/x86/kernel/cpu/common.c
> @@ -617,6 +617,15 @@ __setup("clearcpuid=", setup_disablecpui
>  
>  cpumask_t cpu_initialized __cpuinitdata = CPU_MASK_NONE;
>  
> +static unsigned long long tsc_clock(int cpu)
> +{
> +	unsigned long long t;
> +
> +	rdtscll(t);
> +
> +	return t;
> +}
> +
>  void __init early_cpu_init(void)
>  {
>  	struct cpu_vendor_dev *cvdev;
> @@ -627,6 +636,8 @@ void __init early_cpu_init(void)
>  		cpu_devs[cvdev->vendor] = cvdev->cpu_dev;
>  
>  	early_cpu_detect();
> +	if (cpu_has_tsc)
> +		set_printk_time_clock(tsc_clock);
>  	validate_pat_support(&boot_cpu_data);
>  }
>  
> Index: linux-2.6/arch/x86/kernel/cpu/common_64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/common_64.c
> +++ linux-2.6/arch/x86/kernel/cpu/common_64.c
> @@ -215,6 +215,15 @@ static void __init early_cpu_support_pri
>  	}
>  }
>  
> +static unsigned long long tsc_clock(int cpu)
> +{
> +	unsigned long long t;
> +
> +	rdtscll(t);
> +
> +	return t;
> +}
> +
>  static void __cpuinit early_identify_cpu(struct cpuinfo_x86 *c);
>  
>  void __init early_cpu_init(void)
> @@ -227,6 +236,9 @@ void __init early_cpu_init(void)
>                  cpu_devs[cvdev->vendor] = cvdev->cpu_dev;
>  	early_cpu_support_print();
>  	early_identify_cpu(&boot_cpu_data);
> +
> +	if (cpu_has_tsc)
> +		set_printk_time_clock(tsc_clock);
>  }
>  
>  /* Do some early cpuid on the boot CPU to get some parameter that are
> --
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